Well you can certainly support him, and I'm sure he'd be glad of such support, but the truth is, he must be willing to realise that he has a problem and want to fix it.

If it is bipolar, then he should definitely try to get some help. If you can encourage him to talk to a doctor or counsellor or therapist, that's the first step. If he doesn't want help, you don't have to run away, but be aware the situation will most likely get worse and may in turn cause problems and bad feelings for you, which you don't need.

I think one of the most important things, whatever you choose, is to realise at the end of the day that this is his problem, not yours, and while you can certainly help, you can't fix it without him wanting it to be fixed. You should make sure your world doesn't become entirely focused on him, be supportive, but set boundaries so you're not dragged down also.

You may also want to consider posting in the Caregivers forum... some of the people there will have practical experience in this matter.

Good luck, and whatever happens, you are an amazing person for caring this much.