I would ask your SO if he is talking to SD about HER behavior and telling her she was the one in the wrong and should apologize to YOU.  

Yes, you are the more mature, and as a result, the wiser. You have watched her behavior and that she is disrespectful to others, not just you. Wise and sane people do not put themselves in the path of abusers.

I would tell your SO you understand his concern, you support his relationship with his child, but until you are certain she will treat you with respect, you will remain on the peripherary.

Let me first tell you that I am sorry you are experiencing this. Something similar also happened to me this summer, only I'm close to your age and SD is in her upper 40's, not 20 something like your SO's SD.

If SD did something to you, you do NOT owe her an apology, AND, if SO talks SD into apologizing and she actually does, it will not be an apology, trust me, I know these things. It will be the SD and SO "Dog and Pony Show" ...SD shows SO that she's playing nice, and when you disengage (if that's what you in fact choose to do) then get ready, you will be the villain in this story. On that note, I like what SacrificialLamb wrote:"Wise and sane people do not put themselves in the path of abusers." There's much truth to that.

As for you being the "older/wiser" of the two, I couldn't agree more, however, if SD has "drawn first blood" she will only become empowered and emboldened by it. It's very common for these men to give their wives or SO's "lip service" to appease them, but just know, they are most likely doing the same thing to SD. Then, these men wonder why they feel "trapped in the middle." Well, it's because they created the mess, and tell their wives, "I just want everyone to get along." What part of their psyche thinks that will ever happen? DH's/SO's need to handle thier daughters. "Not my circus, not my monkeys" I'm buying a tshirt with that quote on it!

I  hope you are able to crack the code on SO and SD respecting you and treating you with fundamental kindness, however, I have not seen that mastered yet.

Best of luck, and check in with us!

I am of the mind that the solution is a schedule. You make it.  Fill DH's schedule to the brim and leave very limited openings.  Inform him that the times stipulated for you and he to be together are inviolable and he can fit whatever he wants into the rest of the non work time.  Make it clear that under no circumstances short of life threatening illness or injury does YOUR time get violated.

Tell him to bring a doctor's note if he makes the mistake of testing  you on this.

You come first, the marriage comes first.  Adult kids... nope... never do they come first and since they are adults they are no longer even a marital responsibility.  Their behavior directly influences the daddy time they get and the pleasantness of any part of their lives that are related to you and to DH.

Good luck.

Stick to your guns.

You have clarity; your boyfriend has love goggles. He has a separate agenda (to get you to play Happy Family) and would prefer that you make things easier for him by eating excrement and accepting mistreatment.

 Stand your ground. If any of your boyfriend's people comment about his daughter at the funeral, be breezy and say something like "Poor Sally, she's never had to share her father and seems to be struggling with him dating". Be charming, dress well, and escape after the service.

I’m about 20 years “more mature” than you are. My advice is to forgive and forget. 

But by that I mean forgive her for being such an ass and forget that she even exists.  “Ignore the whore”.  Don’t have anymore conversations about her and try not to ever be in her presence.  Or if you are around her treat her as if she is just something just to ignore. 

Don’t waste your breath trying to justify your actions to anyone.  I know you will want to say that you want nothing to do with her because she’s a disgusting POS.  But don’t. You just have better things to do. 

Believe me it works. I told my DH to keep his son and the son’s GF away from me.  I could make cracks daily about how worthless they are. But I don’t.   My DH can see and talk to them as he wishes - as long as they are no where near me. 

duplicate 

The only way this step stuff works is if the parent puts his/her partner's feelings FIRST, not those of the kids.  If SD was rude/disrespectful to you, he should have put her in her place, and let her know he won't tolerate you being treated that way.  However, for him, her place is on the same level as your place. Now, if you were rude and disrespectful to her, he should also be able to tell you that's not OK. For most of the people on here, the parent puts their kids feelings' first, or at least equal to the partner - so you hear a lot of "I don't want to be in the middle!" crap.

If you've been honest with yourself and do not think that you are the problem in this situation, then stay "disengaged", which means you are polite and civil and friendly to SD if you have to be around her, but it goes no deeper than that.  You don't act like you hate her, or shun her in public or any of that - that's where the maturity comes in.  You just act civil and distant and polite.

I'm fortunate to have a DH who got it right off the bat. He never allowed one minute of disrespect from SS to me.  But that seems to be unusual in these parts.

Also, rethink if you want to sign on for this crap for the long haul.  It probably won't get better.

What your SO is really saying to you is: Forgive, Forget, Repeat over and over while SD gets to play her childish games with no consequence.  I was one of those SM's who fell into that pattern for years, any deviation from my doormat status would result in a fight and accusations about how I hated skid.  Now I avoid skid interactions whenever possible, they are DH's kids not mine and he dealt with them fine before I came along so he can continue his one on one relationship with them.  If drama does (and it does) happen in my presence I'll just act confused and walk away. This is the "Dumb Fox" tactic in the book, "Why Men love B*tches."  I don't take any of their man baby sh*t personally anymore, DH's either.  Like you I am way too mature for the Jr high drama.  

I don't extend olive branches, my present to them is a view of my rear as I walk out the door.  

Why this is just another serving of the shit flavored gaslighting sandwich!  

NO, just stay in your lane, its the one the rest of us sane people are in and let SD have her lane.  She will slip, when she sees she can't get you to misbehave in front of the family, she will let some snide comment slip.  Think of it as a game with her, you behaving so well, forcing her to give her self away.  Less energy for you wasted on this.  

DH doens't have your back with her? Then you make sure she understands that you are on to her your own way.  DH doesn't have to be a part of this.  You can convey  a clear message to SD as you stand by SO, arm linked with his, being the ever suppotive GF, just by looking at her with the right eyes.  If she reacts then you act surprised, hurt and clueless why she would react that way.  I doubt she will, but its good to let those crazy SD's that you aren't going anywhere due to them.  

"SO thinks I need to forgive, forget and give her a second chance."  And you know what happens?  Then it's a third chance and a fourth chance until the pattern is so entrenched, and you get so overly saturated that YOU explode.for   Meanwhile DH gets off of the hook for letting SD know where her role is in this new family dynamic by throwing you under the bus.  Been there, done that.Give DH back the responsibility for parenting his child.  She may be 20 years old but still must be informed of family boundaries - by him.  As for you, disengage from SD.  As others have written, don't bring up SD to DH and when he brings her up, change the subject.  Treat her with distant tolerance at best.

I gave my SD a second chance.  She was nice for a very short time before she resumed her obnoxious behavior - and it got worse.  By the time SD had her meltdown, the situation had become way out of hand.  Today, SD is not allowed in our home and I have no contact with her.  This could have been somewhat prevented if DH had done his job as a Husband and Father.

Your experience is so similar to mine. Please, please be careful! Steps csn be exceptionally manipulative! So much do that they could probably convince the Pope that there is no God! I tried for over 25 years. Nothing changed. I’m a forgiving, easy going person. I’ve been hurt over and over only because I was naive and believed my SDs could change. They don’t. And, they won”t. It is a very complex, deep-seated psychological phenomenon. Only the very RARE stepfamily ever sees peace and acceptance. I finally disengaged. I have nothing to do with my SKs. Nothing. I was  the one who always put on the parties, dinners, bought the gifts, wrapped them thoughtfully. The straw that broke the camel’s back was when I invited my40something SD and her family to my summer beach house for one week. Upon entering, SD never acknowledged me or my home-/only her dad. I cooked, did activities with all her kids, made sure they had a wonderful time. But, I could feel their coldness toward me. After the week vacation, SD sent a heartfelt thank you letter to my husband and had each kid write a special letter—-to my husband. They all thanked HIM for a wonderful time at HIS beach house. I was never mentioned...and, I’m the one who invited my SD and family. That day, I decided to disengage. Being a loving, forgiving person, it was initially difficult. But, I can tell you, it’s the best decision I’ve made re: these toxic people. Save your sanity and wellbeing. It won’t change. Also, I’m an eternal optimist. But, in the case of stepkid dynamics, reality is harsh. I wish you peace. 

I wish I had a dime for each time I cried "I just want PEACE!!" over the years. My impotent words did nothing to change the dysfunctional dynamic of my DH's family. 

 If we want peace, we have to be willing to fight for it. We have to be willing to change ourselves, lace up our bi!ch boots and say ENOUGH. We have to be willing to walk if that's the only way to a peaceful life, and we have to be ruthlessly honest with ourselves about our own and our SOs' culpability in these awful step situations.

I was a doormat for years. I thought if I was patient, tried harder, modelled loving behaviors, was thoughtful and kind, that I could effect change. I could not have been more wrong. As children of divorce, most skids have been catered to, spoilt, and allowed to call the shots. They have zero respect for kindness, seeing it as weakness and merely as their due. What they do understand is STRENGH and WALLS. When we stop trying to reason with dysfunction or fix it, when we let go of the dream of being loved by these damaged skids and instead focus on our own needs, goals and behaviors, we empower ourselves. We start to heal, and gain clarity, and know peace.