"She brought something out of me that I can’t even explain."

        So, why does Edward bother being good ? Because he doesn’t like causing suffering. Even living on the death of the very evilest of humans, eventually all the killing makes him feel purely monstrous, and he hates feeling that way. He wants to feel like himself. He wants to feel the higher human emotions (love for his family particularly) that get lost when you live for the hunt and the bloodlust. He doesn’t think being good will earn him anything, but he still does it, because he still thinks good is better than bad, whether it gives him something in return or not.