An alarm went off in my head when you said he avoids going out with friends on the weekends because then he can’t drink. Does he often turn down offers or events because he would rather stay home and drink? I guess I would ask him if he can have fun and unwind at all without alcohol.
What happens if you go out with friends on the weekends? Does he stay home and drink by himself?
I don’t think you are unreasonable in your request at all. You have put up with it long enough that it’s not just a matter of you getting used to it, you have discovered it is getting worse for you. If he is completely unwilling to compromise then unfortunately you have to ask yourself if you are willing to live this way for the rest of your life. If you do decide to stay with him when he has made this ultimatum, then I would say you cannot complain about it any more. He has given you the choice: accept it or leave. If you stay then you have to accept it.
Maybe you can try one last time to find a compromise, I think counseling would be a good idea. Tell him that you want to find a a way to make both of you happy. If he refuses or counseling doesn’t change anything, then again you have to ask yourself if you can live this way or not. The solution does not, however, lie in dragging this out any more or putting the decision off. That only makes both of you unhappy. Maybe you could give him your own ultimatum - that you two must find a way to make both of you happy. If there is no way to do that (if he is unwilling to change his behavior at all, and you cannot be happy the way things are), then maybe it is time to call it quits.
Good luck - it’s never easy to end a relationship that has lasted so long.