There's nothing I an say that hasn't already been said. I'm actually in a similar position as many here. (I even had a foot fracture while the ABF was MIA) Our story similar. I sometimes wonder if, for me, growing up in an alcoholic house makes that discomfort and disappointment all too familiar. Sometimes I think I go back and keep going back because it's what I know, not really what I like.
My only suggestion is to ask if you really want to be involved and if there's room for anyone else if you are going to be involved as a friend with this guy. It's quite a lot for him to ask this of you. I'm asking myself the same questions, and I haven't yet come up with the right answer. My friends and family sure want me to move on though. I'm not sure I can, and I'm not sure how that would look.
Good luck to you.