I agree with others that she sounds like trouble. But that's not the worst of your problems. I'd be way more concerned about your boyfriend's behaviour here. He is his own person: he was not forced to any of the choices he has made. Or maybe he was forced by her. So either your boyfriend is co-dependent in (what sounds like a) really unhealthy drama-filled relationship, or he is in an abusive relationship. Whichever it is, what kind of room is there for you in his life now that he is living with her?
I don't think I would stick around and wait for the drama to hit me.
Partners with Alec and Mya