Afraid, You've given us bits and pieces, but I suspect he's heard something about that night.
I wouldn't address the matter with him when he's drinking because he will blow it all out of proportion and want to argue with you about it. You know that you can't rationalize with a drunk or someone high on drugs. Now, if he should raise the issue when he's sober, that would be a different story and I would come clean and tell him exactly what happened and leave nothing to the imagination. Until that time arises, leave it be. You don't need to have any more crap on your plate right now.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
