[ericedge]

Given your description, I wonder if perhaps you're burning out due to over-committing to your work. Caring about the work one does is laudable, but if it's the only thing one cares about, it will never completely satisfy, and a passion-then-quit cycle like you describe seems to be a familiar result.

There are plenty of suggestions online for ways to avoid burnout, but it seems like it's even harder to diagnose than prevent, and usually involves a lot of soul searching. I unfortunately don't have any good recommendations for either diagnosis or prevention, but it might be worth considering as a possibility.

If you're not familiar with the patterns of burnout, I found this article to be a good introduction: http://nymag.com/news/features/24757/