I think if you gave it a shot, you would have a good chance at having a successful relationship. Best friends already know pretty much everything about eachother... they are those people that you can be yourself around, no matter what. If you like him, go for it. It would be a shame if you both liked eachother and didn't give things a try because you didn't want to ruin your friendship. What do you think would happen if you got a boyfriend... or if he got a girlfriend? You'd both be happy for eachother, but there would still be a hint of jealousy... plus you don't want to be left to wonder "what if?"