i wouldn't do anything. it's his mess, let him clean it up.
it's not up to you to find a lawyer, it's up to him.
i also wouldn't tell your son. he can do that himself.
try to keep your focus on yourself and your son.
he'll be feeling pretty bad when he wakes. when they feel bad, they tend to drink so they don't have to deal with themselves and what's happened. don't be surprised and have a plan for this....perhaps you and DS can go out and see a movie?
naive