Was there another person present? No.
Was he in bed with someone else when she glanced at him? No.
Was he wearing someone else's lipstick? No.
Was he wearing clothing she didn't buy him? No.
Was his clothing somehow the issue that gave him away? No.
Was it a facial expression that gave it away? Not a facial expression exactly. (I'll admit that's a bit of a trick answer.)
Did she spot him somewhere he shouldn't have been? No.
Is she telepathic but only if she is looking at the person? No.

