For Caine there was 'mated' for splices, and 'love' or 'dating' for humans. He had no idea who Kirk was sleeping with, but he kept his assumptions to himself and would wait to be proven wrong. In the meantime, there's flying to be done. All of that wasn't really vital to know.

Egged on by Kirk's obvious enjoyment of the situation, Caine leans forward and makes a sharp corkscrew just to make Kirk's head spin.

"...Not all the time," Cain said after a moment's hesitation. Obviously he hadn't when he was imprisoned. "But they were my signature when I was a legionnaire! Most legionnaires didn't like to get too close, but I thought it was the most effective way to handle some situations."