Megamind and Metro Man were supposed to be a team.

Megamind and Metro Man's parents knew each other, and knowing their planets were about to be destroyed, they both sent their only son to Earth. The goal was for Megamind and Metro Man to become a team, and protect Earth while inspiring humanity, and leading humanity to basically make paradise on Earth.Metro Man found this out later in his life, and knew that if he told Megamind, Megamind wouldn't believe him. So he kept trying to get Megamind to throw aside his evil ways. His loneliness that causes him to leave, is partly caused by the fact he was a jerk to Megamind while they were kids, and he pushed aside the one actual friend he could have. He shoved aside the individual who would understand where he was coming from.He does nothing to stop Titan, because he wants Megamind to become who he was supposed to be. When he tells Megamind "You know, little buddy, there's a yin for every yang. If there's bad, good will rise up against it! It's taken me a long time for me to find my calling. Now, it's time you found yours." He knew Megamind would become a hero because his parents had told him via a message he discovered.Part of the reason he doesn't help, and the reason he says nothing at the celebration is that he wants Megamind to get that love and admiration from the citizens of Metrocity, that he used to get. via /r/FilmTheorists https://ift.tt/37mAuzn