Is he still living with his family? If he is, is there any friends (preferably sober) that he can move in with? Being around other alcoholics is one of the main downfalls of an alcoholic which can mess up their recovery.
Being there for him is the most important. Just be as good of a friend as possible. Listen to him, talk to him, and make sure he knows that he is cared for deeply and has someone to go to if he ever needs to talk to anyone.
If you are willing, tell him you have your phone on at all hours and that he shouldn't hesitate to call if he is scared, lonely, or upset, or even just wants to chat. Having that should be a really reassuring support system for him.
Also, if you want, maybe you could try attending some AA meetings with him (even if you don't have a problem with it yourself). Going to these alone can sometimes be scary for some people, especially for the first few times, so he might like the support. If he'd rather go alone, at least he knows the offer is out there and that you cared to think of it for him.
I am sorry about the loss of your child, by the way. That must have been terribly hard on you.
Feel free to PM me if you ever want to chat. My dad is an alcoholic and has been through over 15 rehabs, so I have been through this before many times. I know it's tough, but you are doing a GREAT job of wanting to be there for him and be such a good friend.