Honestly, I don't fault Kamijou for anything he did or didn't do in the series at all. I don't think he was grossly insensitive towards Sayaka simply because he didn't immediately tell her that he was discharged from the hospital, or didn't immediately seek her out at school. He was on a pretty strict time schedule considering just how fast Sayaka had a mental breakdown and eventually died over the course of the series, and then there's the fact that Sayaka might not even have been his only regular visitor at the hospital, which would remove pretty much whatever reason Sayaka would have known for being a top priority...
And for what it's worth, it's not even a guarantee that Kamijou wouldn't have returned Sayaka's feelings. For all we know, if Sayaka confessed, Kamijou would have accepted and they'd both live happily ever after. I just don't see him as the evil villain who crushed Sayaka's heart and spurned her affections at every turn from being a total insensitive twat like a lot of people seem to.
edit: this picture made me laugh though