You want closure, you want an XYZ explanation on why this relationship didn’t work out.
The answer to that is pretty obvious, it didn’t work out because of untreated alcoholism. I don’t really think it’s about you needing closure or being selfish I think it all comes down to this…
I just want to know he cares
I’m sure he would not have stuck around for 3 years if he didn’t care for you. It’s not like he consciously asks himself, do I pick lostinjersey1 or do I pick to drink. He is so consumed by his disease right now he couldn’t possible comprehend the damage or hurt he is causing you. And not that his disease is an excuse for unacceptable behavior because it is not. But rather more for you to understand that this is what life is with your alcoholic. He could get sober tomorrow and he could stay sober for 30,60,90 days or more but the odds of this experience you are going through right now repeating itself is extremely high.
Often loving an alcoholic is to run out of tears. I'm sorry you had to go through this experience.