Should I break up with my boyfriend?

I clued him in that my heart's not all in it anymore. I found myself becoming interested in someone else with more ambition and intellect and I don't think it's fair to him to keep him in this relationship when another guy might possibly (but not for sure yet) take his place in my heart. However, he doesn't want to let go. He keeps telling me he can change the things that I don't feel are compatible in our relationship. I don't think compatibility can be "fixed" and it just is. He tries to make out a lot when we're together but the conversation and intellectual stimulation is lacking. I keep telling him that sometimes even if we love each other, that isn't enough to keep us together. He told me his world would fall apart and I feel terrible because he has no friends anymore. I don't want to leave him alone but I shouldn't stay out of pity so.. what to do?