Your son sounds just like me as a young man.
I could get sheepskins from colleges (3), but segueing into the real world of work, accountability and responsibilities was more than I could take.
I developed GAD and my depression (probably endogenous) got really bad.
I went to a couple of doctors and got meds (this was 35 years ago, back when tricyclic meds were the only antidepressants being widely used), tied them, quit and continued to drink and take benzo's.
My drinking and benzo plan didn't work out very well (to phrase the matter gently).
I ultimately gave up trying and went through treatment for my substance abuse problems.
I sought help for my depression and GAD 10-11 years later and finally became free of the daily symptoms of my problems.
My alcoholism has been resolved (at least on a daily basis through the AA program) and the meds have eliminated the symptoms of my depression and GAD.
I agree that your son needs treatment for his alcoholism.
The treatment personnel will also address his other problems.
I wish you and your son the best.
Keep us posted.