Dealing with people who are bi-polar

I have a friend who has these mood-swings, and I don't know if he's bi-polar or not, but whatever he has certainly mimics this disorder. For instance, he's currently mad at me and says that he's taking all connections to me out of his life. At this point, he has disconnected me in some ways but is still connected in other ways. This kind of thing has happened before, and we've gotten to the bright side of things again, and I'm expecting it to turn out the same way this time. Even so, every episode hurts a lot--and it especially hurts in how he truly IS a good person. In his case, I don't know if it's post-traumatic stress syndrome or bi-polar behind his mood swings. He's a brilliant person with a big heart, and there will be people out there who won't have the patience with him like I do in the role of a very close friend. We aren't related, but he's one of those people who's like family to me, and I don't want people to write him off when he has a lot to offer.