I would make it crystal clear I wasn't interested, I would say as an addict I have been prone to stupid things that did not reflect my true feelings.
Also all my friends are of the opposite sex, very few have made and inappropriate advances, in fact I would say I have been hit on by just as many of the same sex so...

Tell him you will see him if he is sober and in. A public place. Just so he really understand how far over the line he was.

Take care.