u/Sharp_Giraffe_1529

My 21 years old sister brought her boyfriend over for the first time while I was in my room. She had no idea that I was at home, so she didn't mind how loud she was talking. I started eavesdropping through the vents and heard her boyfriend say, "Take off your top". I got excited from hearing that, and then I could hear him asking her to suck his dick. At this point, I wanted to sneak a peek at her room, but it was too much of a risk, so I continued eavesdropping through the vents. They then started fucking, and I can hear her moan loudly, begging him to stop. I got turned on so hard and cannot stop myself anymore. I started masturbating to my own sister's moans and the way she and her boyfriend were dirty talking. I came when her boyfriend started moaning, he's coming onto her face. Later, during family dinner, I noticed she looked tired, and her hair was a bit rough, but I couldn't look at her the same way, knowing I just came to her getting dicked down.