Welcome!  First, you've done nothing wrong.  You have been misteated, your bf hasn't stood up for you and you're doing something healthy, disengaging from someone who hasn't treated you well.  How to disengage?  Keep things polite and civil with her but don't do anything special for her.  She doesn't want anything from you and won't appreciate it.

I had a similar situation with my youngest SS, now 57.  When I disengaged, I stopped driving him around to all his sports, stopped initiating conversations, stopped discussing him with DH.  I was polite and civil and did the same as for the other kids, cooking, laundry, etc.  At bdays and Christmas, we spent the same on him as the others but DH chose the gifts.  Frankly, SS and DH seemed to prefer that I'd stepped back.

Can things improve in the future?  Maybe. YSS57 and I still have a polite, civil relationship but we aren't close.  On the other hand, I was the problem teen and my stepdad disengaged when I left home.  After some years went by and I matured, we got close again.  So, it can happen.

Good luck, keep reading around here and search disengagement for more info.  Glad to have you here, LifeIsTough.

Nothing worse than a bratty teen SD emboldened by her parents.  I included her father as he should have had your back.  It's a double betrayal by SD AND your BF.

Just how much are you relied upon for financial help running the home?  You could renegotiate your contribution by making him pay 3/4 and you pay 1/4.   ( him and his two, you pay for yourself).  Is marriage on the horizon?  Unless you two can be a united front against the world, BM and her little minions will be able to cause problems.  The couple should come first.  Period.  I think you have a BF problem.  
 

Disengaging , in my opinion, works best when you just stop doing, are to busy to participate and take care of yourself first   Announcing it can put a challenge out there to test you and  see if you mean it   You don't need that   She's already testing the waters with her power move   
 

At 15 , you can also explain if she asks why the change,   you are just giving her what she wants, asked for.  There are some lessons only a stepmom can teach.  This is one of them.  BTDT.     

First, welcome.  I hope that you find this to be a good place to vent, contribute, and to pick up some useful perspective from others who are living the dream of the blended family adventure.

Now. Why was BM in YOUR HOME?!  Never again. Your BF's  baggage has no place in your home. At least the XW element of his baggage.  Mommy sitting on YOUR sofa stroking this toxic crotch product's hair while the little succubus lied her ass off should have never been tolerated.  As for the toxic Skid, she is a kid. She does what she is told when she is told otherwise she can STFU.

BF needs clarity that his baggage will no longer be tolerated to be a detriment to you living your best life.  I suggest immediately implementing very firmly enforced standards of behavior and standards of performance for this kid from the moment she arrives in YOUR home until the moment she departs. If that ends her visits, good riddance.  She is 15. She is not a young child. She is a young woman and her infantile bullshit needs to be met with zero tolerance.  Her baby bullshit and lies nave to end one way or another.

IMHO 

Take care of  you.

My queston is what the heck, "...but I was ridiculed this one evening, out of the blue, while her mum sat there supporting her by stroking her hair the whole time while I was intimidated."  !!  Why was BM there!?

Keep on with the disengagement. You are doing the right thing. It sounds like the BM is stoking this which is why you need to look up "parental alienation", i.e. PAS. If the SD is so far gone she's already pitting mom's house against dad's (god forbid there should be rules and expectations to follow) there's not much you can do.  Except remember this is not your fault! Dad should have absolutely been upholding rules and expectations himself too!  If you were the fall guy it's also then squarely on HIM. PAS is hard to fight unless it's identified very early on and the targeted parent knows what to do to counter it. He still can, but it's almost a losing battle.

Just remember this is not you and everything must come from your DH.

I've been through it, you can read my blogs. OSD pretty much never set foot in the house and spoke with DH a handful of times after age 13/14. I refused to compromise and do what OSD wanted (which was to do what she wanted always) and DH didn't step up. OSD is now almost 21 and has no contact with DH. I feel zero guilt. Even with the PAS, she knew what she was doing, still does.

I reiterate the question - Why was BM in your home? where she had no right to be.  As to the rest of your situation - it sounds somewhat similar to mine.  A couple of years ago, SD29 spewed a lot of toxic shit at me over a long period, and I have concluded that I am the easy target.  Her mother and father give her money and reinforcement for being what she is, ie an entitled, aggressive, borderline personality disordered person.  I give her nothing so am fair game for being the punch bag for all her resentments, of which there are many.  Cover1W mentioned PAS - here is a good article on it: https://www.goodtherapy.org/blog/child-or-weapon-psychological-dynamics-...

Good luck, and remember  - it's NOT YOU!!!

Biggest problem i see is your "partner" failing as a partner and as a father. He should have never allowed this to go on. With BM. In your home. He is clearly giving BM too mich control over your lives. No telling how long it took BM to get the little Harpie, Jr., all worked into a lather and brave enough to do this. So much is wrong here. After this many years with this guy, this happens. It will take much counseling to undo whatever bad patterns have formed that led to this being allowed. He should have set his child straight right then and there and set BM straight like a decade ago.

Please prioritize yourself. Someone needs to. Whatever it was that Harpie Jr. was complaining about (please say it wasn't you watching your own television) needs to be addressed by your partner. 

"I now want to 100% disengage but, how exactly does one do this with no upheaval?  How do I disengage at christmas and birthdays without it being awkward? I really hate awkwardness!! The 10yo i have a fantastic relationship with.  I aim to maintain it but am fully prepared if it ends up being another round of this."

The way to disengage is do it steadily but stealthily. First of all, get your mindset in the right place. Keep reminding yourself that SD15 does not want a relationship with you nor do you want one with her. The only thing you "owe" each other is to be polite and civil when you must see each other. That's it. That's all it's going to be from now on.

The next thing is you need a sit-down with your partner and tell him in no uncertain terms that you WILL NOT finance any portion of SD15s expenses.  No buying (or paying for) her clothes, special meals, decorations for her room, even feminine products, That's entirely on him. Keep your money separate from his. Do not let any of your hard-earned income go towards a petulant punk who could care less if you live or die. Also tell your SO that you will be polite to SD15 and expect the same from her when she is in your home. If she cannot be polite then he must correct her or she will no longer be welcome, and he can meet her out of the house somewhere.

ONLY IF YOU WANT TO ...When it comes time for holidays give her a small  impersonal and very inexpensive gift - like what you would get for a grab-bag at the office (a pair of cute socks, a small box of chocolates, body lotion, etc.)

If/when SD comes over, you will politely say hello but will not inquire/ask her about anything. Then immediately find a convenient excuse to do things in your room, out of the house, or even something special you can do with SD10. (Try to keep your relationship with SD10 positive BUT don't be surprised if she joins forces with BM and SD15.)

All I can say is teen SDs are the worst. They often develop an attitude which will never get better and they will always consider you an interloper because of their blind loyalty binds to the BM. Mine is like this and she's married with her own family  So are many, many others here on STalk. Once in awhile one may break free of BM's indocrination when they reach adulthood but it isn't often, and it often isn't permanent.

Girls ages 13ish to 17ish are at a difficult age to the point of being insufferable even for their bio parents. If there is a circus master BM in the background and your SO doesn't have your back then you are being set up to fail, big time. I also think it is very challenging for women without children to have sympathy for their SK's and SO messed up situation.

Your SO needs to do for his own kids. They don't want you to do for them because they prefer their parents do stuff for them.

Your work is to stop ruminating and wasting time, emotions, energy on this toxic waste dump. You being consumed by toxic step sh*t will in no way make you a more interesting person or a better person. You have to train your mind to ignore the circus and instead focus on yourself. What are your dreams, passions, interests, hobbies? Focus on those. Spend time with people who actually value, appreciate and care about you.

If your SO can't grow to the point of the plus side outweighing the con side, then he may be the wrong person for you. I know that many women find that dating men with children just isn't worth it. There are so many men that have no clue how to handle their ex, kids and a romantic relationship.

And you can not win.  BM is not allowed in your home. No iff or buts.  If SD never step into your home again...thsrs ok...

'You can not win playing SDgame it's rigged.,   When or if [ it doesn't matter ] SD steps into your hone again.  It's. Hi SD. abd that it .  No cooking for her. That's up to DH, no cleaning,,no contact with her.. it's your home.  The tv is yours. You watch what you want . When you want. 
Actually SD should stay with BM. 

"I have a really great relationship with her" - can you really still believe that after what happened in your home?

"as does my BF with her – " - this i will believe. It wasn't him who was attacked, though whatever goes on with his daughter while on his custody time is his responsibility, not yours. You were scapegoated for his failings, even if his only failing is to teach his daughter to be respectful of adults and grateful for the work they put into caring for her.

I know you feel you are a "chill" person, but damnit you need to heat up a bit over this! You matter just as much as your SO, his daughter, and his ex. As long as you are polite and respectful to the kids, and don't get in the way of your SO's relationship with them, you are doing great. And notice i said his relationship with his *daughters.* You absolutely can get in the way of his relationship with his ex. Actually, if you even have to, that means he is too enmeshed with her to be a real partner to someone else. 

Welcome! You have definitely come to the right place. I have been disengaged from SD14 for about 4 years now. It has been so much better since and I don't regret it one bit. I was losing my sanity and disengaging has helped me take control oover the situation. 

Our stories are VERY similar! I have known SD since she was 5. Very much did the same things you did, bought gifts, helped with homework, took shopping, made dinner, pick up/drop offs at school, gymnastics events, etc. I definitely took on that role. As SD got older she threw it back in my face around 10 y/o. Saying she didn't want my help anymore, making up lies about myself, being disrepectful and rude. I stopped doing anything "extra" for her. I was still polite, greeted, etc. But no more parental roles for me. 

Start deffering SD15 to her Dad. If she asks you for a ride? Go ask your Dad. Asks what's for dinner? Go ask your Dad. Makes a christmas or birthday wishlist? Go ask your Dad. Eventually she will get the hint. SD14 has also taken out her anger on my DH now. She argues with him constantly and does not want to be at our house. Funny thing: when I was still involved, I got the blame for SD14s bad behavior. Now that I'm disengaged, it's much more freeing. I can't be blamed for things I am not involved in. It's sad that DHs relationship with her Dad has gone downhill, but it is out of my control. 

Stay strong and don't budge on the boundaries if they start asking for favors again. It's not fair to SMs to be used whenever it's convenient for SKs. In my mind, I was either all in, or all out. I'm all out now. 

Thank you to all who have posted, I am learning from your experiences/responses.

I am curious, has anyone entered a relationship when the SKIDS are adults? How did this go? Good, bad, disengaged? I am eager to learn more.

I have 100% disengaged from OSD and at 'polite and cordial' with YSD. YSD32 is quiet and hard to get to know...though I have tried; she is also socially awkward and not thoughtful when communicating (for example, bringing up her mom all the time along with OSD). She is fairly intelligent but lacks EQ. She is used to people 'doing' for her. I am not willing to do that for anyone, especially someone who lacks gratitude; my life is full already, plus I brought my kids up to be independent and they are, even though they are a lot younger.

The expectation that SM's should wrap themselves into a pretzel in order to seamlessly fit in, put everyone else's fee fee's abover her own, and in no way change the dynamic of the failed 1st family is pretty engrained into the societal messages about being a SM. The media loves to portray DH, BM, SM, and SK's all smiling widely for the camera at juniors baseball game or whatever. I have found that those who knew the failed 1st family before it's collapse are especially dedicated to these bizarre, insane and impossible expectations.

God forbid that SM *doesn't like* her Sk's. I personally am beyond not liking mine, I can't stand them. They make my skin crawl and I have lost a certain amount of respect for my DH. Although SDiablas are not very much like him I can see the role he played into creating the monsters they have become and it's a pretty big f***** turn-off. Overall the good outweighs the bad so I am willing to deal with it, at least for now.

This idea that SM should be the person SK's want them to be is so stupid. I was also accused by SK's of not being enough like BM and BM's female friends. I am reserved, calm, thoughtful, introspective .... BM is none of these. She uses big, impulsive, over the top cliche exclamations and exudes fake enthusiasm. She is a big manipulative phony that wants everyone to think she is richer, smarter, and better than everyone else when the opposite is true.

SDiablas told DH that they wanted me to be more outgoing like BM. Well, la ti f**** da, too bad. I like who I am and I am REAL. I am not and will never be anything like their crap BM. My kids are not and will never be anything like SD's. Thank goodness. I have a close, healthy relationship with my children. BM and the SDiablas fight like cats and dogs to the point of physical violence. They are so weird. Maintaining the 1st failed family is the least of my problems. Some of DH's family doesn't like it that I don't like SD's. I invite them to have a closer relationship with the Diablas themselves. Lol

" This idea that SM should be the person SK's want them to be is so stupid" Amen to that, sister and that BS never ends. 

Its is absolutely ridiculous ( @LifeisTough, just bear in mind how unrealistic  it all is so dont beat yourself up. )  YOu are far from alone.

I will never get why these SKIDS think they are so important as to swoop in acting as if they are an authority over you more than yourself. That grinds my gears like crazy.  Who do they think are?  what gives them that right to tell you who YOU should be or what you should do?? The irony is that this is coming from my SD29 who I know doesnt even know or LIke herself. Keep in mind that its usually the most Insecure people who expect you to change for them so that their needs are satisfied.  Then they go on to try to compare you infavorable to themselves and others.  I got sick of hearing about how DH;s cousin treated  his stepkids as his own. and even more of how SD29 is being "Stepmom of the Year' ,,yeah..right...to her fiances brood, finding me lacking. As if I care . I wanted to say, well them maybe you should have married or gotten adopted by DH;s cousins friend, etc. if they are such a perfect StepParent! As for SD, perhaps she needs to focus more on her bio kids and "steps" if she thinks she is so much better than me in that area.

You know its nothing more than a  weak ass ploy to try to make you feel like a failure  for disappointing them. Its like they assume that if they guilt trip you enough , then you will revert back to falling  over yourself trying to please them by fitting into this image that They created for you. . Its like it never dawns on these enittled Skids that their made up version of me in their effed up minds is No longer my responsibilty to live up to.  May I continue to disappoint SD , MIL< even DH or any of his other relatives if they object. If they wont ever see the error in their ways from placing expectations on us without our permission, from trying to limit me into their narrow views knowing I dont want to play along with their created narrative, then thats no longer my problem either. All they are doing is just making me dig in my heels even more, .they are embarrassing themselves the more they try to push me and only driving me away further

What you see is what you get.  Just be thankful it happen at 14. Look at all the money you will be saving.   If SD want to stay with BM. That's ok,  you don't have to be putting up with her.  DH has to pay more CS .  That's on him for not parenting his kid correctly..

'Make DH. Understand that you are disengaging from her.  You will be doing nothing for her. Her Christmas gift is a $50

- gift card.  Her birthday gift is a $50 gift card. "If she luckly." She doesn't get any additional gifts or clothing.  
'You will read the CO.  And it will be followed to the letter of law.  If DH objects. He can get a additional part time job to fund her.

If Daddy -daughter. Trips.., meals ..vacation...party's.. are not listed in CO. They don't happen..,if family vacations are not listed in CO. They don't happen

You open a bank account in your name only.   Any additional funds SD gets . You bank account get the same. I,e,  SD get a happy meal at McDonald for  $5. Don't think this is in CO.  $5 goes into your bank account.  
'There will be no graduation party's.  No car...no college expenses unless mandated.  No wedding money   SEE DH abd part tine job. And he funds your bank equally.

This is war. You did your best to mark it a family and SD disrecept you.  Don't ever think she will change.  Your DH is at fault for allowing this disrespectfull mess to happen 

Wow your SD14 sure gave you a laundry list of complaints. And now, IGNORE. Full on ignore, especially if you and DH have tried to include her in activities and she's completely not joined in. We did the same thing when my OSD complained about "not doing anything" so we started inviting her and making plans. Not once did she join, she would have rather stayed in her room - again. It wasn't really about her wanting more time with DH or us, it was about her getting to do what SHE wanted to do and if she wasn't interested or it wasn't her idea she noped out of it. 

Anyway, there's nothing you can do about her attitude towards you. You keep on doing your thing, don't let her stop you. Don't listen to any more laundry lists - but if somehow you get roped into one then you fire a laundry list right back at her. I believe that teens need to hear the truth right back at them, that's how they will learn! Don't be mean about it, but stick to the facts. My SDs couldn't ever really argue with me because I was a truth-teller and they couldn't argue! I refused to argue with a 13-14 YO. 

And of course, she doesn't care that you are there or a part of the family then fine, she gets no support or involvement from you. That's a real ramification of actions. I don't have friends that don't like me, the relatives that treat me not so well get a modicum of attention. Why would she be different?

Teens regardless of gender are only difficult and behave like shit when they have shit parents.  Hormones shmormones.

The advice about regarding not surrendering space in our home to a shit spawned ill behaved rude SKid is absolute brilliance.

Fill the space.  When kids are well behaved, they can join and enjoy that space. If they are not well behaved and are constant drama generators they get "Get up and give me the remote."  Every time we want our space, they vacate it.  Regardless of if they were there first and watching the TV when we want our space.  Period. Dot.

Winning their game and playing it as we choose forcing them to play our game sends absolutely the right message IMHO.  If they get their fee fees hurt and complain, they get asked how they like the new normal and and how they like being treated as a minimally tolerated nuisance?  Highlighting that their rudeness has consequences.

Tolerate no bullshit.

To disengage.  All you have to do is live your life your way.  

FIRST OF ALL.  Where is DH...the BF..in this.  He let his kid disrespect you that way?  He didn't say or do anything. That's your big problem l
 

It's your home, you pay the bills, clean fix that home. SD means nothing to you. She made that clear. Since SD doesn't like you. That's ok . She gets the same in return.  You don't like her. 
'There are peope I don't like.  I just don't associate with them. Buy them anything.  Do anything for them. If they show up, that's ok.  If they don't show up that also ok.  I don't invite them any place.

 If I buy a pizza. I get it fir myself, what I want in it. If they get a slices or not not my concern. If SD gets a slice or the dog gets a slice it's the same to me.   It's your DH problem. He let it happen.  He can't expect you to invite someone who doesn't like you on vacation.?