Hi Kathy,
Splendra and Ann gave you good avice about the alanon and naranon meetings.
I think its important also not to be an enabler in any way.
Your son is 20 years old and he needs to start making the right decisions for himself now. Of course he is not happy where he is right now, but, the only way he is going to get the message is when he has to fend for himself. You only need to be there for support.