I think you're doing GREAT, and the emotions you are feeling are perfectly normal ones.
The only caveat in terms of "buying you out" on the house--make sure you aren't potentially on the hook for the mortgage. If he can do it, you're right, that would really be the best. The RE market isn't so hot right now, so whatever gets you out with the least muss and fuss is probably a good decision.
Look, you have made your decision to leave for all the right reasons. Hopefully, he will embrace recovery and get well, and two people will go on to have happy lives--separately.
My Al-Anon meetings were a lifesaver when I was preparing to leave and move back across the country. I wish I'd stayed involved when I got back, though--maybe it would have helped to prevent my own slide into alcoholic drinking and a brand-new bad relationship (with a non-alcoholic). It was like I made my escape and then screwed myself over by making the mistake of thinking that all my problems were over once the alcoholic was out of my life. Instead, I handed my fate over to another dysfunctional person and to the bottle.
Keep your eyes on the prize!