@Kyonko802 Don't get me wrong he killed a lot of people, but Omni-man was clearly trying to work out his true feelings all across that final fight with Marc. The fight ends with Marc battered, unable to move, and Nolan just leaves because he can't stand the emotional pain he's inflicted on himself hurting the few things he had truly come to care about during his time on Earth.
He's imperfect in a very human way, trapped between a rock and a hard place, and the only real difference is he can upend buildings with a wave of his hand.