Michele James, my stepsis, believed she could sneak away with her boyfriend for a gym quickie, but she underestimated her stepbrother's voyeuristic tendencies. I catch them in the act, her big boobs jiggling as she bounces on him. My cock hardens at the sight, and I can't resist the urge to join in. I confront them, and Michele, seeing an opportunity, switches partners, climbing off her boyfriend to straddle me. She rides me, her big tits in my face, her hairy pussy contracting around my cock. I fill her with my cum, marking her, turning her cheating into my advantage.