A Matter of Time
Sam learned a lot about Jack O'Neill, the officer and the man.
He could carry a grudge - he had been shot by the enemy then left for dead by his teammates and supposed friends. Then he was captured and spent four months in a hellhole of an Iraqi prison. She could understand his bitterness.
But he was also willing to sacrifice his life for the greater good.
Was it part of his personality or was he still suffering the psychological effects of his son's death?
Maybe he couldn't quite grasp the scientific implications of the gravity wave and its effect on the rate of time but he would step up when push came to shove. O'Neill may have been bitter about Cromwell but he wasn't a fool. O'Neill had worked with Cromwell in the past and they could again cooperate in the operation, jump the wormhole, save the planet and hopefully not get dead in the process.
Earth and everyone one it was more important than his long held grudge. And he knew all too well they both might end up like Henry Boyd or worse.
They were awaiting Teal'c with the nuclear device. O'Neill took Carter aside away from prying eyes. He held her and whispered in her ear "You know I don't totally get that space- time- gravity bending thing, but I do know know that all we have is now." And he kissed her.
He walked off as if nothing happened, handed her his tags and put on the climbing harness.