Al-Anon might help you re-frame your thinking away from shame at not being able to help him quit drinking to accepting that you never had, and never will, could, or should have any control over his drinking at all.
You're not going to go to Al-Anon to be berated over all of these perceived failures. You'll go to be understood and accepted by lots of people who made many of the same choices you did and who learned to forgive themselves.