Maybe you can’t do anything about his drinking.
Maybe he will have to create a great deal of misery and heartache for himself before he will pull up.

The one thing you can do for him is not cover for him. Let the ramifications of his actions fall squarely on his shoulders alone.
There is a school of thought that only a great deal of pain will cause us to stop drinking. That was the case with me, and I have found that that is the case with a lot of other people.
But you’re his mother, and you love him. You want to shield him from hurt. It is natural, but it may be the worse thing you can do for him.
There are young people’s AA meetings, Find one. He might identify with people there.

Good luck,
Richard S.