She lets him feel her ass because it's the only feeling he's going to be doing for some time. If he keeps up with the way he is, she's not going to let him have anything even when they get home and she doesn't care if he hears her think it. She knows that he won't leave on the off chance that he can make her do what he wants her to do. She has the advantage here, though she knows it won't last forever.

"Because I say so." She slides her fingers along his jaw, brushes his lips, and then pulls away.