She has a habit to make him change his attitude and decisions by being suggestive, yet she then always lets him down. He liked her for most of his life, including after hitting puberty, so her invitations would have been a huge deal for him. Yet she never delivered. When she's too often deceptively seductive, it's natural for the dude to fire back at her like that, even if he didn't truly believe she has been sleeping around. She brings this upon herself. Not to mention she's also otherwise pissing him off continuously.