Lily Potter neé Evans, wife to James Potter, discover Peter Pettigrew, one of James's best friend and member of the order, thinking of defecting to Voldemort. She confronts Peter and tries to persuade him, claiming that their side can support him too. As their talk heats up, Peter lashes out and asks even having his virginity taken. Which Lily firmly agrees to. This leads to Peter and Lily fucking. Which becomes a routine thing. Somehow their frequent fuck sessions is what leads to Voldemorts loss.