I am in a similar situation. I REALLY like this guy, he has a great personality and everything.. but he drinks and does drugs. But I am willing to give it a try because I like him that much. Hopefully I can help him through it and get him to stop? But I would say just give the guy a chance.. and if you do end up getting together, let him know your feelings about it and let him know you would feel better if it wasn't done around you.
Quitters always lose, and winners never give up.