Well, the fact that he admitted drinking heavily during your separation would seem to be good grounds for you to ask the court to require supervised visitation and/or alcohol monitoring during visitation periods.
The fact that he seems to want to be kind toward you suggests that maybe you can wind up with an amicable divorce. If he's said he wants out of the marriage, then I think getting things wrapped up in a way that isn't bitter or hostile would be to everyone's advantage. If he was sober for 10 years, then he presumably knows what he needs to do. It happens. I've been sober in AA for 8 years, and I know people who have had relapses after many years. Some come back in, redouble their efforts, and are fine--all the wiser for knowing what lies ahead.
ETA: I always think it's a mistake to try to hold onto someone who has said s/he wants to leave a relationship.