the problem with this dude is that he is wacked in the head. if he were at least halfway normal, you could go beat him to a bloody pulp and not have to worry about much. but he sounds pretty unpredictable. if he has no value of his own life, i'm sure he doesn't value yours much either. if you know any cops, have them fuck with him. a restraining order won't do shit. if i were in this situation and didn't know any cops that could fuck with him, i'd get guerilla-style on his ass and attack the fucker while wearing all black with a ski mask or something to cover your face and no witnesses. who knows, if he's so suicidal, he may even like it. hehe. if you really want revenge for what he did, you gotta bring yourself to his level.
as for the girl, don't let your emotions get the best of you (as they already have....now you're involved with this freak too), be her friend, give her advice, but if she doesn't want to leave, then there's not much you can do.