It was the breath on his ear that did him in. He hadn't known, until now, how sensitive his ears were, and having Ellie panting and moaning in his ear was potentially one of the most stimulating sensations he'd ever felt (with the obvious exception of actually penetrating her).
He let out a low groan, feeling his climax hit. It was the first time he'd had an orgasm caused by another person, and he intended to savor it. He quickened his thrusts, all but slamming his hips into her.
A thought struck him at the last moment that actually made him cry out in shocked pleasure. He was coming, inside her, and he wasn't wearing a condom. With a strangled grunt he imagined emptying himself inside her, wondering if he should tell her what he was thinking. It was... pretty out there, after all.