Don't even think about speaking to her like your bf suggested. What would you say? You'd just be supplying more fuel for her to hate you. 

How about talking to him...? As she has a significant inheritance coming her way,  start talking about her getting her own place with the money, how exciting it will be for her, etc. Don't ask, say these things if it were obvious. Tell him he could help her find a really nice place how much fun it will be helping her to decorate it, and so on. Work on getting him understand that this is what adults do.

You don't have an SD problem, you have an SO problem. Do not talk to this girl. It's not your job and it'll let her know that her tactics of over powering you in your own home are working. It is up to your SO to deal with her and he seems like a ball-less wonder when it comes to his DD, so the prognosis for him dealing with her is slim to none. Your SO is being a shitty SO expecting you to eat shit. Your SO is a shitty SO for telling you that you should be the one to talk to your SD. A real man would tell his bitch of a DD that she must show respect and that you are not going anywhere. Your SO should have her on a launching plan or to at least have some requirements, but instead he is her slave. 

Your SD is a mini-wife. Mini-Wfe Syndrome occurs and gets enabled and even perpetuated and facilitated when there is a weak father. Mini-wives don't reach milestones when their peers do, so don't count on her moving out any time soon. She has been given all the power, so she's marking her territory and letting you know constantly that she's no. 1. That girl isn't going anywhere. Even if she did move out, mini-wives have a way of ramping up the contact and the domination of their dads from afar. My SD34 had her skype open with my DH 24/7 in her apartment, despite moving in with her first BF, whom she didn't get until she was 25 damn years old. That relationship didn't last because the BF didn't want to "live with DH," which is how it was with skype open between DH and SD 24/7 for CONSTANT contact. I almost left DH's ass because it drove me insane. Mini-wives don't change. My DH changed because I almost left his ass twice and we both went into heavy-duty therapy, both individual and martial. I went to heal the part of me that resulted in me being in a marriage in which I was the inferior female. DH went to delve into why he fostered a mini-wife and why he was so scared shitless of his own kids, especially SD. While my DH changed, it took ages but SD never changed. She still attention seeks like there's no tomorrow and DH has to constantly be on his toes and handle it because he knows that I won't tolerate being a distant second to any female, let alone that PoS. 

I would move out. If you don't want to break up with your SO, at least downgrade your relationship and move out. Tell your SO that you will not live with him again unless and until he handles his DD and his own issue of why he doesn't stand up to her and why he sells you out. Tell your SO that a man not having your back is a deal-breaker. He has a lot of nerve expecting you to live in misery. He'll keep doing it if you don't issue major consequences. Yes, it ultimately could result in the demise of your relationship, but do you want to be treated this way and feel like this for a long time? 

I went epic on my DH, but I was at the stage of being more afraid of spending the rest of my life the way I was than of losing my marriage. I even had 20 years in the game. Before that I would go only so far and then pull back out of fear that I'd lose DH, but every time I pulled back, it let DH know that I wasn't serious and he could continue to allow an insane mini-wife to live with us and torture me. It's beyond soul-destroying to live being a second class citizen to a mini-wife for any lenth of time, never mind long term. Move out and maybe go for some therapy so that you can accept more than crumbs for love. You deserve better. Make your SO prove himself. I'm so mad on your behalf and he knows you're miserable yet wants you to continue living there in the same house as your abuser. And yes, what she's doing to you is abuse.

To be honest, I'd pack my things and go. There are way too many red flags here. Remember: You cannot change someone else. 
I could never be with a man who thought it was acceptable for his daughter to send provocative photos of any kind or who would make jokes about his daughter "pole dancing." The primary issue here, as I see it, is him--the father, not her.  

Love can't thrive in isolation. It needs so much more for a relationship to work well and be healthy. Sometimes we just have to walk away even when we know it hurts. You've only a few more years with your son being a minor, focus positive energy on him rather than wasting energy trying to engage with an adult woman who clearly doesn't want anything to do with you. 

Your boyfriend doesn't sound like he really cares for anyone but himself. He misrepresented or ignored his daughter's true feelings about meeting and living with you. He insists you chase after her (so you don't move out) rather than attempting to be a mediator and addressing his daughter himself. He doesn't care that you're uncomfortable, that his daughter is uncomfortable, he just wants everyone to "get along". If you hadn't raised/hinted that you might move out then I doubt he'd be doing anything. 

Read up on enmeshment, aka emotional incest. Often it's rooted in family trauma, like when one parent dies and the other becomes emotionally dependent on their kid(s). My late FIL was enmeshed with his daughters. This happened after he and MIL divorced and she became an alcoholic. The kids came to live with him, he spoiled the girls rotten and they ran the show. The enmeshment continued until the day he died.

We've had other people join ST because they've been in similar situations, recognize it's abnormal, but can't put a name to what they're witnessing. Now you know, and I hope you'll hit the eject button. It's all dysfunctional, and this man isn't actually emotionally available. Life is too short to waste living with a mini wife who hates you, and even if she were to move out, the enmeshment would continue.

The butt and body pics and pole dancing comments are gross and not normal for a healthy father-daughter relationship.

She is a hard core mini-wife, they are super hard core enmeshed and what is occurring is emotional incest. You have an SO problem. SD is just a product of his dysfunctional behavior. She sort of knows better, but she benefits from all this, plus shes going to be well off soon, so everything is going her way.

He will not change. It works for him.

She will not change. It works for her.

I seldome say GTFO, but he wont change. He brought you in under false pretenses, shes his wife, you are the sidepiece. You want to be the main event here, so leaving the situation and spending more time and energy on your DS15 is the best way to go.

Glad you made it on here - this sucks!

I agree with those who say spend more time with your son. Whatever time you gave up to be with this guy, take it back and then some. You will never get this time with him back. I found myself making that mistake in the first year or two with my SO, and i regret it. You could devote 100% of your time to this SD, and she won't see you as a mother figure and she won't stop sending sexy selfies to her dad. Her dad will likely still not set boundaries or have her move out, even when she is an independently wealthy adult. You will have wasted that time, and your actual son will appreciate you. If you stay with this guy, do not sacrifice yourself or your family for him. He won't sacrifice his for you. 

Seriously

These creepy big daddio /daughter relationships are sealed in stone. The enmeshed duo are unbreakable.

You will always be the chick on the side and the daughter is the wife.

You deserve better. 

Like seriously its creepy AF to send your daddio a pic of your arse. RED FLAG , abort this man.

You can do better

Blessings

First, a 20yo needs to GTF out when a man and woman are starting a new partnership.  20 is an adult.  Barring any mitigating circumstance, she has no business living with her father and his new partner.

Next, it sounds from your original post that his first wife or is she the XW just passed.  If it is the XW, no worries. if they were still married, how long ago did she die?

As for this over sexualized mini-wife pimping herself out to her own father... nope. Do yourself a favor and leave him in your past. NOW!

If  you decide to go forward with a relationship with this buy, mandate that his prior family progeny leave immediately. She is not a minor. Also, when her inheritance pays to her, no relationship resources from you or  her daddy should go to her.  She has an inherritance. She can live on that, go to school on that, invest that, etc....

IMHO of course.

Take care of you.

Run, fast and do NOT look back.

What a creep.

I thought I was the only one dealing with so and daughter having a questionable relationship. First they share a bedroom when i met him. There is just a king size bed in the room. She acts like a jealous girlfriend and has mini wife syndrome. During an arguement she yells at her dad " she dont even suck your dick!"   

I never worried if someone was sucking my dads dick and how would she know? Unless they discussed it. I think they have sex to be honest. 

I left and you should too. Its toxic and it will never change all you will do is waste your time end it now and let them live together like the couple they are. 

I was going through this exactly 4 years ago. It was sickening to see the sultry looks and bare booty pics DaughterWife would send her daddy. He kept tellng me to talk to her because he wasn't man enough to confront her on her ignoring me and being a slob around the house. When I would tell him the photos are very inappropriate to send to a father, he just didn't understand or want to understand. I walked in on them being too physically close and that was it. I hope you can move out and date him, only seeing him when she is not around, meet him at restaurants or spend time away together. It would be interesting to see if they text each other non-stop when she knows you two are together, or drop drama into the dinner/date with you to get all the attention and ruin your time with him. I hope it works out for you, getting yourself and your son away from that little witch is the first step back to having freedom. He is the problem for allowing this to happen and she won't change.

I would run away as fast as possible from this man. I'm sorry but this is NOT normal behavior between a father and daughter. It's not going to change. Get away from this dysfunctional duo asap.