Guilt
Edward has a long time running affair with guilt. He wallows in guilt. There's plenty of it after all; guilt over failing to bring back his mother, for nearly destroying his brother, for making Winry cry so many times. He feels guilty about Hughes' death, and his inability to save Nina; for letters never written, promises broken, words never said. He feels guilt about what happened in Liore and the things that were done to Rose. Then there's guilt over joining the military against everything Izumi taught him; for the agony and irritation he has caused her. He's trouble for everyone he knows.
The ironic part is, he's not all together sure he doesn't enjoy it in some sick way. Guilt and he are old friends now, constant companions that travel together well. Perhaps its not healthy. Perhaps there are ways to deal with the guilt, get past it, but he doesn't really care about those. Edward doesn't mind the guilt. For all the things he's done, he deserves it. He feels guilty about 'that' too.