He is so sweet when he is not drinking. Why can we make it work as friends but not in a relationship??
Because when you're friends, you can choose when you are together. If you're tired of him, you can say "I don't have time today" and it's all good. If he's drunk and mean, you can say to him "I don't want to hang out with you when you're drunk and mean."
In a relationship, you don't have the same flexibility. You also tend to feel responsible for your partner in a way you don't with a friend.
Are you crazy to think it would work? As long as he's drinking and not in recovery -- YES. You're crazy to think it could work. You can't have JUST the nice sober guy. The other dude, the one you don't like, the drunk? He's part of the package.