"No, not at all!" Why would licking his own spending off her belly be a punishment? He gets to touch her, it's a reward. Especially as it brings his face right beside her undies, which seem too fancy for a librarian. Out of her price range, unless it's a luxury she saves for...Or a gift. It occurs to him that he should have asked before if she's even available. But if she's willing to makeout with him and jerk him off, then she probably is...

"...Although I should apologise." He smiles, but certainly that apology is in it.