1. He doesn't give up, break down, or go crazy when he finds himself inexplicably a year in his past. Instead, his almost immediate reaction is "now I can fix things".
2. And this is because he's spent the past year (and actually most of his life, come to think of it) rehashing his mistakes and coming up with all the ways he could have avoided them, and is willing (glad, even, in a twisted, ironic sort of way) to sacrifice his own personal happiness in order to ensure the safety of Atlantis and the people now inhabiting her.
3. Though him being miserable won't actually help matters at all, which he does realize. Eventually.
4. He tells the Athosian kids Batman stories (suitably edited for Pegasus) instead of Freddy vs. Jason or whatever it was he told them in 1x03. (He tried Spiderman once, but that didn't go over as well.)
5. Instead of trying to do it all on his own, he goes to his still-living commanding officer and tells him the truth, complete and as unbiased as he can manage. And does so knowing there's a good chance he'll wind up in a straight-jacket (or the Ancient equivalent). He's accomplished the main thing already, though: that first, preventable death that quite probably set them on the path to all the other.
At least that's what he tells himself while he waits for Sumner to finish reading his report.
[[...that is, I think that's how it's going to go. although he could maybe get them through a couple near-crises before realizing he can't manage it without at least one ally. yes?]]