I agree with Mamaof3 on just about everything she said above.
He was honest....I would give him credit for that. At least you know what you are up against. Some people ....in fact MOST desi/muslim people wont tell you about their past or current habits/experiences. It is only until after marriage that you find out about their bad habits.
The past is the past....most teenagers and young adults experiment with different things be it drugs, alcohol, cigs, sex, dating, etc. It does not mean that they are a druggie, alcoholic etc. Many give up soon after trying it and others dont. Like mamaof3 said....who is to say that the non-experimental man that you marry wont want to experiment later on in life? I know some couples who have tried out things together after marriage....whos to say he wont want to do that?
Personally, I wouldnt want my marriage to start off on the wrong foot. I woud want it to be in the right path according to my beliefs. However I wont judge a man based on his past because it isnt necessary that his past behaviors will effect his future negatively.
Look at some key traits that he has.....the things that you are looking for in a spouse and go with that. Get to know him...dont rush into it. Hang out with him and his friends if possible.....see how he acts with them. Get to know his buddies....you can learn a lot about a guy by the friends he keeps.