I'm glad at least that the other party guys know that he was in rehab and that they say they support him. Maybe they recognized that he took the "weekend snort" to a darker level and had concerns about him...who knows...they might be relieved that they are not "responsible for him", they might be happy that there is "more for them". Even though the conversation wasn't scripted the way you envisioned it...it still happened. They know he was in rehab and they support him...
If they want to continue to party, they won't really want him around. And it sounds like he doesn't want to be around them either. Also...don't be a bit surprised if he starts to get "inquiry calls" from other weekend warriors who are starting to possibly sniff out a little help...the "what is it like?" call.
Other than that...are you going to meetings? Do you have a program? It's great that you reached out here...and are open to others perceptions. You are going to need support. I am guessing you feel fearful, protective and vulnerable. Don't forget you are powerless...
Get your program up to snuff! You will need your own contract with yourself to stay happy, joyous and free!!
Praying for all the best for you and yours!!