What should I do? Idk what kind of reverse psychology to do. My best friends fianc� is abusive. ?

Here's what happened. I got back in touch with her and we hung out. And she told me her fianc� didn't like me (aka my step cousin) he has no reason not to like me. I have never done ANYTHING TO HIM. So I sent him a message saying there shouldn't be any reason why we can't all be friends and so on. And then I asked him in person if he got the message I sent and he said yea, and that everything was cool. And I said ok. Then the more me and Sarah hung out, the madder he got. She kept telling me she wasn't allowed to have friends because he wouldn't let her. I never tried to make her leave or stay, I tried to give her encouraging advice that she's a grown woman, and tht if he loved er, he would love all her friends, and would be happy for her to hang out with them as long as she informed him. I would never let anything happen to her. And then one day he came to pick her up and was speeding down my driveway with babies playing outside. I live in a small trailer park. And our co-landlord whatever said he needed to slow down the next time. So I told him then. Then the next time both Sarah and I told him. He said I don't give a f***. And did it again. And now he's banned from my house. Then she took me off of her Facebook. And I called her and asked what's going on ad she said he did it. And that she wanted to hang out with me. I said Sarah, honestly, I'm afraid that one day, maybe not soon, but one day he might hurt you and hit you. And she said you really think he would do that. And I said honestly one day, yes. And she called him and told him she was going with me ad called me back and said please come get me. I'm about to hit Craig. He threatened me. So I called my husband to go get her cause I was shopping. And later on in the day, I told her to call her grandma and she called him. And we were all going to meet at Arby's and talk. And when he showed up he pulled her of by herself and was talking to her. And I walked over there and said are y'all coming in? I wanted to