I stumble upon my stepsister having sex with her boyfriend and film them for my own pleasure, leading to a mutual masturbation session

I was wandering around the house when I stumbled upon my stepsister and her boyfriend in the act. Being a pervert, I decided to secretly film them for my own pleasure. As I quietly watched, the guy's massive tool plunged deep into her tiny, natural tits. I was captivated by the sight and found myself stroking my own dick. Little did I know, she noticed me and beckoned me over. It turned out she was okay with the idea of having a threesome. She eagerly took his monster cock in her mouth while I pleasured myself. The sight of her sucking his big cock led to a squirting orgasm, leaving her dripping wet. The guy then took turns with me, fucking her in missionary position, driving her wild with pleasure. Finally, he released a massive load on her beautiful face, leaving her satisfied.