I think girls have really bad self esteem so they don't think they can get better so this guy comes up to them and is really nice at first (he has to be to get a girl) but once she's locked into this relationship the guy starts acting like a total jerk. Of course, he pays attention to her (not positive attention) so she enjoys that in some messed up way. And he can be nice to her, sometimes..but most of the time he's just a jerk. However, she thinks so badly of herself (and he makes her think even worse of herself) that she just stays with him.