Mom isn't breaking up with crazy boyfriend

When my mom started dating me and my sister didn't really like him but she still dated him, but now my mom is realizing that he isn't the person she thought he was. When ever my mom comes over to our house he will call her alot, one day he drove down and sat on the bench on our lawn and my mom had to talk to him. And the other time he called her and she just left because she said she had to because she loves him. I ask her if he's hurting or threatning her but she says no, she says she wants to leave but she's scared her parents won't let her. But I'm woried that he might hurt me someday when she comes over or breaks up with him.