Their last night wasn't what McCoy expected, or at least the last night they'd have until this could be undone, if it could be undone. He figure Spock would have wanted to use the opportunity for sex, and he really didn't object to that idea. But as always, Spock surprised him. They didn't talk much at all, maybe they didn't need to.
There could be no apologies between them, their world didn't admit that kind of weakness.
So there was just a silence, not uncomfortable, but not easy either. And touching each other slowly. Nothing more than they hadn't already done, but different all the same. Knowing it could be the very last time.
McCoy hadn't wanted to sleep. He wanted to lay with Spock and watch his chest rise and fall. But he had no control over exhaustion, and eventually it claimed his time.
He woke up with a sense of dread. Which more than likely was from the knowledge that he was about to change hands yet again, this time to Marlena's whim. And who knew what she would do to him before she gave him back to Jim.