Cloud was supposed to be depressed. The whole point of the movie was getting over his inhibitions tying him down and moving forward with his life along with the people he cared about.
I hate this overused term of emo for actual mental instability.
Crisis core was his original self where he was an affable young man but still dejected over not achieving his dreams and promises. In FF7 he was a guy who thought he was everything he really wasnt, overlaying someone else's personality onto his and all kinds of fucked up. And in AC, he was as stated, at the end released from everything that had come before.
Its called development people