Personally he comes across to me, as a self satisfied and selfish person, who only wants to continue as is. If someone told me he would only come back home because his lease was up, and not because he wanted to work on our marriage.....I would tell him to go sign a new lease.
As for his hanging up on you, contact when he wants and weekends with just the son, is any one of these an intimation that he wants to be back with you?
I wonder what his reaction would be, if you said you thought he should continue to live in his own place.
I know divorce is not pleasant, having been there myself...but neither is supporting someone who really is not interested in reactivating his marriage, and you could do without having to fork out financially.
I also don't think counseling every 3 weeks is worth much, even if both parties are working hard on the relationship, and spending time with each other.....once every 3 weeks????
If he is not in a recovery program for HIS drinking then he aint in recovery, and yes if he does come home, he could very easily relapse and blame it all on you.
May I suggest you give this deep thought, and maybe see a counselor yourself, one who understands addiction, and can give you help with decisions you have to make.