Like many posts of this type its mainly about the alcoholic.
What are you getting out of this relationship now?. Did you yourself grow up seeing alcoholism and heavy drinking?.
You may well love this man but his primary relationship is with drink and his thoughts centre on where the next drink is going to come from. Alcohol is a cruel mistress and this is a relationship that is going nowhere for you except downwards. Two years on you need to ask yourself the awkward question as to why you did not leave 6 months into this relationship. It was never a question of he seeks help and from that he would quit drinking altogether as you have perhaps supposed would happen. There are no guarantees when it comes to alcoholism.
He may well be "functioning" but for how long now?. He is not really functioning and you're basically propping him up. He could well go onto lose everything and everyone around him and could still choose to drink afterwards. You have choices to make and you need to make better ones re him than what you have chosen to date.
Why do you feel guilty here?. This may be all a part of you being in such a codependent and dysfunctional relationship. I doubt he feels guilty as to how he has treated you. Do you really have a good life with him; I doubt it very much. He spends probably most of his day drunk or on a comedown from alcohol.
The only person who can help him here is him. He got some help but these efforts of his were not maintained. You've also told him you were going to leave but have not followed through with this and you are still there for your own reasons. You are really as caught up in his alcoholism as he is and you're still there playing out the usual roles associated with such people. Your roles here are enabler, codependent partner and provoker (because you never forget). Being like this neither helps you or he and you enabling him gives you a false sense of control. You also need to get off this merry go around named denial before he continues to drag you further down with him. You do not mention children thankfully; do not ever have a child by him.
Getting support from Al-anon for your own self is a must do; at the very least you need to read their literature. I would also suggest you read a lot more about codependency in relationships because that is really doing you no favours either. His needs are not more important than yours.