It could be that he looks at all the things that need to be done, goes "Aw crap. Where do I even start?" and then gets frustrated and overwhelmed, leading to inaction and the subsequent guilt over inaction.

In the non-profit I run, I find that I have to come up with a list of things that need to get done; then I sit down with my board members and volunteers and we prioritize and then divvy out tasks. It takes some time, and my board members are still not particularly good at taking action when needed, though they're getting a lot better), but all of our stuff ends up getting done more or less where/when it should.

The other possibility is that he realizes he's in way over his head and wants to go back to something safer/less demanding.

It seems like you're pretty loyal to this fellow and that you want to keep him around. The thing to do, I think, would be to give him a more concrete sense of direction and see how he responds to that. If he doesn't respond well, then it might be time to have a frank discussion with him and to search for someone else to fill that role.