I said this in your other thread but don't know if you saw it, but it applies here as well:
"I think many addicts would like to have a "normal" life. That does not mean it's possible when they are in active addiction and he has realized that. The choice is alcohol or a normal life with a nice person.
He chooses alcohol and probably, really, sees no other choice which again you will understand more about as you learn more".
He can't have a relationship with you and be an alcoholic and drink as much as he wants to, so it would seem. This way he gets to keep you in his life and drink as much as he wants. Also, it keeps you on the line, he doesn't have to worry about you wandering off with someone else if he keeps you engaged in this relationship (I'm guessing).