A domestic issue, what do you think of this guy?

I have a friend who is dating this guy. He has a son with someone else but my friend is just now finding out about it. Basically this guy lied to her about that other things. But he still keeps calling her. The other night she told me that a guy tried to talk to her a gas station and her boyfriend saw it and he got so upset with her. He basically threatened her and called her all kinds of names. But yet he told her she was his number one girl. I don't know what to tell my friend. I'm honestly scared for her. I don't know if he really cares for her or not because he'll say all these weird and hurtful things to her, but at the same time he's always trying to be with her, he calls her all the time and like the other night when another guy tried to talk to her, he got so angry. When she says she's leaving him, it's like he'll play it cool like everything is ok but then he'll turn around and ask her like "for real, so you leavin' me?" like he's not sure. It's like he says it's okay for her to leave but he stresses the point of questioning her about it like is she sure, like she really shouldn't do it. But I don't know, this is a serious issue, what do you all think?