Hi Charr, sorry you are in this situation and getting hurt.
Yes, most relationships with alcoholics don't start out the way they become. Alcoholism is progressive and when he picked up that first drink again, he was right back where he was. As you probably know, alcoholics can't moderate their drinking, one or two is never, ever, enough.
So you are faced with a bigger dilemma now because you have had that sober time with him and are well and truly attached to him.
Your boundary, to not be in a relationship with an active addict held when this first came up. He left, got treatment etc. That boundary you have was for a very good reason. Don't let yourself down now. This is harder because you have been in this relationship longer now, of course, but the boundary is still a very valid one, no?
Boundaries protect us. It's a good idea to have them so that when we get in to a situation where they apply, we know what to do. We know the decision we made (with good reason) while not in the throes of an argument or in the situation, when we were clear thinking.
I wouldn't listen to his drunk rambling, it has nothing to do with you, it has to do with his alcoholism. Yes, to an active alcoholic EVERYTHING is boring, except drinking and doing whatever they want to do. It also clouds his judgement and other thinking skills. Not sure if you have ever been drunk, but imagine trying to run your life from that place.
You are trying to come between him and his drinking, that never ends well.
Perhaps time to dust off that boundary and let him go off and do whatever he is going to do, which may or may not include getting sober again.
You didn't Cause it, can't Control it and can't Cure it (the 3 c's).
What do you want to do?