[ Kirk nodded his understanding, even if he had never had a very serious relationship in his life. ]
I can't say I know entirely what that's like. Jumping around the universe into the great unknown doesn't exactly encourage long term relationships.
[ He flashes the other a wry, teasing little smile. He respected that Jack was taken, but that didn't mean he wouldn't flirt and tease the other a little. He seemed open to it, and he was certain they were both on the same page that it was no longer serious, just an aspect of their natures. ]