Ummm. I’m not sure how you know he has borderline personality disorder (is this something he told you?), but what you describe certainly fits some of the characteristics. This disorder is one of the toughest to deal with, both as a friend/girlfriend and medically. Don’t think you can change him, because thats impossible. I’ve never been in that situation (I mean as a boyfriend of someone with this problem), but I doubt I would be able to put up with it for too long.