They fucked my best friend's ass because she lent me her phone for a bit

My best friend's hot chick roommate was always flirting with me. One day, she lent me her phone, and I caught her in the act with her boyfriend. They were going at it doggystyle, her skinny ass bouncing with every thrust. I watched, my big dick getting harder by the second. When she noticed me, she just winked and kept riding him. Later, she confessed she loved the thrill of being caught. Now, whenever she needs a favor, I know exactly what she wants in return.