[Affectionate teasing is fine. Hugging and even some kissing don't need to feel like anything more than close friendship, and Chekov has been okay with being Kitty's friend. He's worried that he won't be if this happens. He did, after all, start his only serious romantic relationship in the City with a curse.]
Fair enough. [Now he's overthinking and making this a bigger deal than it needs to be, so he smiles back, puts a hand on her cheek, and kisses her like he means it. Which he does.]