Cheating on my girlfriend with my stepsister

The stepbrother was sying on his stepsister and she didn't notice, later the guy suddenly came up and scared the stepsister, she, in turn, thought that something had happened, but the guy reassured her and asked how she was doing, during the dialogue the sister asked how he had business with his girlfriend, it turned out that his girlfriend was boring, continuing the dialogue, the guy couldn't ask a question of an intimate nature for a long time, but then he decided, it turned out that his sister was acting in porn, during the dialogue the guy admitted that he had a hard penis on her and this strange, later the girl called and the stepsister came close to his dick