Guy troubles....:(?

soo. there is this guy he's soo sweet were going out and im his first gf. were 15 and like im moving and i just can't stay with him. he's a great guy....but im moving and there is going to be fresh meat and a lot of hotties....and i know i would end up cheating on him and i def. don't want that to happen. because he's a really nice guy. but if im in a relationship with someone i have to see them! any ideas how i can break up with him without totally crushing him?