"Not because I had given up on him but because I felt myself falling apart. My head knew I could not fix this. "
You didn't do anything wrong! You handled the situation with as much grace and understanding as you could possibly do under the circumstances.
Didn't seem like you had a choice honestly. I applaud you for being strong and sticking to your boundaries in the relationship.
It hurts of course. You are grieving the loss of a dream and you miss that great guy you thought he was. But truth is he is also a man who relapsed, made horrible decisions and has to pay the price. You also maybe saved his life. If he is locked up, he can't drink.
It takes a strong person to make such difficult choices.