I'm sure it has been shocking and upsetting for you, but to me this situation looks fairly hopeful. He has identified his problem at an early age. My first husband got sober at 21 and he hasn't had a drink in almost 36 years.
Of course, that doesn't mean it will be all smooth sailing, but I think it's very promising that he reached out for help on his own and that he is doing what he needs to do to get his act together.
Having him at home wouldn't help either one of you. This is something he has to face alone, but having a loving family rooting for him--especially with a dad who is a good role model for recovery--will help immeasurably.
Don't for one second let yourself entertain guilt feelings. You couldn't have done anything to prevent it. Better he discovers and deals with it now, rather than years down the road when his life is more complicated, possibly with a family to be responsible for.
Hugs!