No, he obviously couldn't. And what lie was she trying to tell him that made her realize she couldn't? He looks away, not wanting to face her accusation because it's going to force him to admit something he doesn't want to, one way or another.

It's either face it or watch her walk away, though. Peter takes a faltering step after her, then curses and grits his teeth. Nothing for it. "I'm not!" he calls after her. Slightly more quietly, he elaborates. "I haven't fucked anyone else. Not for a month now."

Give the boy a trophy.