Smarie...to my way of thinking, the most appropriate place for him to be on a Friday night is in an AA meeting and the fellowship of others who have sobriety as their top priority.
All the other excuses just underline that he is willing to put other things as a priority over his sobriety.
You can probably make a case for him that is about one hundred miles long about why going to the party would feel good to him tonight.
He is not your child that you are trying to make sure that he feels good inside....
He is an adult that needs to learn how to delay gratification when the stakes are high.
His decision, in the end, about what he wants to do--and the consequences are his to bear..whatever they might be....
Your decision to decide if you want to say yea or no...and the consequences of that are yours to bear, also....
***you can't block all pain from his life...no matter how hard you try...