Do I owe my boyfriend an explanation for my breaking up with him?

I dated my recently-ex-boyfriend for a few months. Over the past few weeks, I realized that some personality and value differences preclude any long-term prospects. When I broke up with him, I didn't give him any reasons why, and that really upset him. Do I owe him an explanation? Would that help or hurt our chances of a cordial relationship in the future? If I should talk to him about my reasons, what should I say?