[Oikawa sighs in relief. Sure, he's not completely convinced because he's been in the same room as the two of them, but Yamaguchi's stuttering denial means he's at least pretending not to be interested which is good enough for Oikawa's purposes.]

Aaaah, I'm glad! I thought you might have decided that he'd make a better date than I am. He is taller than I am after all. [Which is the most attractive trait for any volleyball player's prospective dates to have, obviously.]