If he lets go, he doesn't know when he'll get to have this again, so he stays. It chips away at the wall he's resisting being built up in him. He doesn't want to isolate himself and he doesn't want K to be alone, either, and here they both are, trying to be there for each other.

"Thank you," he murmurs. "For not shooting me."

He's said this to multiple people before, but never to anyone who wasn't a survivor of the same plague.