i think you should give him a go. If it works out and you completely forget the other guy then that's great! If you still have feelings for the other guy, then make sure you let the other (nice) guy know.
How is it rebound if you never went out with him? crushes come and go-yes even 2 year crushes. Give nice guy a go and make sure you tell him in the beginning of the relationship that you want to give it a try and if it doesn't work then that's that. Remain friends :)
-Anonymous