Thank you. [He's relieved. No kiss is worth losing a good friend over, and Kitty deserves to be loved by multiple people, anyway. Not all of that love needs to be romantic. Maybe, right now, Chekov is only qualified to love Kitty as a friend. Maybe that's what she needs.
This feels like the place to say something to lighten the mood, but, since he doesn't have anything, he just rubs her back.]