So he wants her to move in with daddy when he should be preparing her for independence? Seriously? He wants to make her even more dependent? Why doesn't he love her enough to teach her how to be an independent, decent, self-sufficient adult? What he is doing is soothing his guilty conscience and making HIM feel better but actively hobbling his child. How effin' selfish.

Your SD has a poor character. Some people overcome this through good parenting and some don't-especially when parent's don't set the example or follow through with consequences. SD is manipulative in a dangerous form-the lying, stealing, and cutting sound pathological. Why our spouses are suckers for this, I never understood. They are desperate for a relationship that does not and will not happen. Her lying about dad's abuse on social media is telling beause there is a permanent record that has been publicly shared. These are major behavior and manipulation issues. I had a similar situation and stuck it out. It sucked the life out of me--unbelievable stress, frustration, and anger. Since I was the evil stepmother, I was helpless when DH did not stick up for me. You have a new baby and with SD's current character disordered manipulations, you would need to be hypervigilant when she is in your home. Without your DH's intervention with SD, it will only get worse. While there is time, try and find a place for SD to live that is not where you are raising an infant. My situation changed after 15 years and I had quietly decided to leave and get a divorce if he let her disrespect me one more time. Over the years, she manipulated DH out of $80,000, stole my valuables and DH's. She lied and lied knowing that if she was not directly caught in the act, all she had to do was stubbornly stick to her lie. It was just a sickening life. In 15 years, I saw my SD get worse. Yours sounds so similar. The years can be long and unhappy where this kind of girl is allowed to live with you. These men need to take off the rose colored glasses. We are NC with SD now and though it hurts DH

, he does realize that she is no good in our lives.

So you're not locking your bathroom in order not to upset her dad?  That's kind of like him not telling SD's mother she stole so as not to upset SD. Stand up for yourself! Inform your boyfriend that you will be locking up your stuff because his child is a thief.  Inform him that you and your child will not be spending any time alone with his daughter because she is a liar who makes false abuse allegations and you refuse to put yourself and your child at risk. (I'd suggest cameras in the house, too). Inform him that his adult daughter will NOT be living with you after she turns 18.  If he gets upset and does not prioritize you, you'll have a much better idea of what to do with this relationship.  Trying not to "upset" him is not the right approach.  

putting locks on  your room. Lock up the whole house, web cams, web cams, web cams. Everywhere other than the bathrooms and her bedroom.  Get her on camera from the second she enters your home until the second she leaves.  Toxic failed family progeny rarely ever stop being toxic. Structure her existance in your home and life accordingly.  

Make it crystal clear to your SO that she will not live in your marital home as an adult. Ever. PERIOD DOT!

Set boundaries with her and her father.

Why the heck are you worrying about upsetting your SO by putting locks in place when their absence is upsetting YOU. It's pretty simple actually, if he doesn't want locks in his home then he'd better damn well start parenting his offspring and teaching them not to steal. Until he perfects that, the locks will stay.

Protect you and your belongings and stick to your guns. His incompetence as a parent does not override your right to privacy and not having sticky fingers in what is yours.

Divorce with teen or adult kids should be excited to time alone with the wife and his kids branching out towards independence. My husband is about to retire in early 2025, he's made it clear to all his skids who are now (18, 25.5 and 27) that when he retires, he's moving overseas to retire with us.

that they had ample time and opportunities (especially sd's to manage a relationship with us instead their petty vindictiveness and disrespect caused issues) so he is prioritising us and our young family who require his presence more since elder 3 kids refuse to meet up and make time for outings (sd's are the worst at this), ss comes back with us for holidays etc

"My therapist says she displays bahavious and temper troubles, that it will get worse if she isn't set boundaries."

To be fair.. your therapist should not be giving advice or try to diagnose a person they have never met.. and to whom they have never seen any of the behaviors.. just your version of them.

But.. you do have a storm brewing with your DH's idea of his daughter living with you when she turns 18.. why is that? is she not going to college?  no plan to be independent?

I mean.. some of the stuff you mention is not terribly unusual.. a preteen being upset/embarassed that their father is  having a baby? acting out a bit over it?  totally normal.. but it should have been reinforced that the things she was saying were not polite.. and that he expects her to understand that she is the child.. and she doesn't get to make these decisions.

the makeup thing?  It sounds like the door was cracked when you helped her use your  makeup.. and she "borrowed" it.. it was also a clear time for her father to in no uncertain terms explain that she needs to respect the property and privacy of the adults in the home.. 

I might have been inclined to buy myself a nice makeup case and keep it out of sight so she was not able to have access though.

But.. the biggest issue is this looming move in.. and why he thinks that is going to happen.. why he thinks it should happen.. and a time to set expectations about what you need and want too.

You might be surprised about the cost in the south lol. A few years ago I worked for a company in Aix-en-Provence. Well, they decided to decentralize from the Parisian region towards our place. So, all these engineers decided to move south, thinking that they'd be able to afford huge houses on their Parisian salaries. They were shocked to find that accommodation was no cheaper than in Paris.

I also have a daughter studying in Nice and the cost of a room in a shared flat is astronomical. But that's the Riviera for you. The proximity to Monaco probably doesn't help either.

While no one likes to deal with an upset partner, you avoiding conflict will not solve the problem. Understand that YOU are not the CAUSE of the conflict. Your personal things have been stolen, and you have every right to be upset about that. You have every right to lock away your own things. I would just set that boundary,  not ask for permission.

If your partner acts like YOU are the problem here, then he's prioritizing his daughter's comfort (and his own perhaps) over yours. That's no way to live.

I have SD23 Feral Forger who lives separately since she ghosted us at 18. She has moved in with Toxic Troll BM a few times and stolen checks, and cashed them against various bank accounts, lies continuously.

Shes asked twice to move into our home and have her "old room" back. The first time, she was told by Husband "you need to work things out with Clove", Crickets then a nasty series of texts. The second time, she called MY phone, demanded to speak to her father and when I refused to hand my phone over, told me that she needed to live with us for a month. No asking, no apologies, but when I asked her how would that work since she hates me and said all these horrible things to me, she hung up.

Her father subsequently told her no.

She had thought it was solely his house, so I had the opportunity to tell her I was half owner too. Like that should matter, but anyways.

SD sounds very disordered. Protect yourself with nanny web cams and with locks on everything. And make a point of mentioning why you are doing so.

These behaviors are not being dealt with in an appropriate manner and will eventually get worse over time. SD23 Feral Forger started stealing around 17 yo. Before that she was rude and mean, told lies, and was verbally abusive. She got so much worse.