As a child of alcoholic, I appreciated honesty and a listening ear.
Maybe don't bring up this "resolution" of your still-drinking husband, but perhaps maybe more generally share information about what alcoholism is and how it works.
I really thought my mom's drinking was my fault for years.
Making it clear that it isn't is invaluable.
I also agree that learning the lesson of "actions speak louder than words" will serve your son in many contexts beyond having an alcoholic parent who says he's quitting while drinking heavily daily.
Wayne Kritsberg "The Adult Child of Alcoholics Syndrome" was a book a therapist shared with me in early recovery from my mom's drinking. It isn't 12 step, but it might be really useful as it explains some of the dysfuntional behavior that builds up in families dealing with drinking, and offers some solutions.
I read the book in my teen years, but it may or may not be right for you son. At any rate, if you can find a cheap used copy or get it from the library, it is worth a look and possibly to share with him.
Getting him out of the alcoholic environment was a precious gift--be proud of yourself for taking that difficult step.