first of all, it sounds like he is bipolar but how does he know for sure? I'm just curious because he might be saying it just to suck you into his "downward spiral" or whatever you want to call it.
Secondly, there really isn't anything you can do. It depends if he really wants help. And sometimes people have to hit rock bottom before they figure that out.
Thirdly, I know it sucks and it sounds like he's hurt you badly. I personally haven't gone through anything like it myself but I'm living with bp, too, so I hope my comments help in some way.
-TP86