Your step-sister was away all summer with the stepcousin you don't get along with and she comes back she asks you about your summer and accidentally exposes that she kissed the stepcousin. She sees that you are getting sexually aroused by this so she talks further about how when they would make bets they would become more and more sexual. He would grind between her buttcheeks, they would kiss, she would give him blowjobs, but they would never have sex until she reveals that she took him in her butthole on the last day and she shows you her ass where he came in that very day. You have been cucked by your step-sister.