Advent Children totally backpedals Cloud. It's silly.
Relapse tends to happen a lot. He didn't actually have time to learn to cope with his issues.
He got his head put back together and then rushed off to save the world.
Psychological ***sticks with you forever. The key is learning to minimize it and striving to keep it that way. I doubt anyone on the team was qualified to help him deal with his ***.
EDIT: I should clarify that I don't think Cloud to be some amazing character. But he doesn't deserve to be ***on by everyone like he tends to be.