He 'lost his virginity' [=he had sexual intercourse for the first time] when he was in college.
(..) -How we're not virgins now. We deflowered each other. We have each other's flowers. Sorry. I'm just happy. I didn't lose my virginity to you. Wait... What? I lost my virginity to Cassie Duval. Excuse me? You said you were a virgin. (..)2017 Lady Bird