I like this premise. I hadn't considered that Superman might leave after he was welcomed back, but Clark has a point. Everyone turned on him too quickly. Superman is so overpowered that he can't operate effectively as a superhero without overwhelming public support. On top of that, Clark's feelings have been deeply hurt. Everyone hates to be scorned for being different and to feel isolated and alone. Knowing for sure that there is no one on Earth that is remotely like you would compound that immeasurably.

"It is a remarkable dichotomy. In many ways, Clark is the most human of us all. Then...he shoots fire from the skies, and it is difficult not to think of him as a god. And how fortunate we all are that it does not occur to him." -Batman (in Superman/Batman #3 by Jeph Loeb)