How do you break up with someone who you dont want to break up with but dont have the same goals?

i have been with this guy for about 2 months and i really like him and everything but we do not have the same goal. he wants a short term realtionship and i want a long term relationship. he said we wouldnt break up for a while but that one day he knows we will break up. to save myself from heartache i think i should leave now. what do you all think