The best life is an interesting one. Remember you could be bored!
Rule 1 with any kind of depression is 'No depressive drugs'. This means no alcohol. Which means
no alcohol. It's amazing how much trouble this simple rule saves. *nod*
The moments to work at are the ones where he is less depressed, not the ones where he is most depressed. Bring some joy to some of his upbeat moments.

And bring a willingness to work on the other problems, especially the financial problems (research, brainstorming, etc.) to the others. Having an aim to work towards is useful against all kinds of depression, especially if there are small successes along the way.
It may be he needs the next job to be as all-consuming as the last, but you have a chance to at least be there as part of it from the beginning. If he can be content with a less consuming job than the last one, you both gain every which way, but again if you're there at the beginning you will be involved with it, not protected from it.
Spike