We were three male students sharing a 1.5 room flat. The half room which was an enclosed balcony was my room. The other two guys shared the main room. We had a rule, if one of us was going to get lucky, the other two had to leave the flat no questions asked. One night I woke up to the sounds of moaning and groaning. My one roommate had gone home to his parents for the weekend and I had gone to bed early. My other roommate had come back from a night out with his girlfriend. He decided not to wake me and took her to the lounge for some quiet fun. My half room/ balcony had a glass door to the main room and one to the lounge. I used to go through the main bedroom to the toilet as it was the shortest route, which is why he took her to the lounge. Half asleep but aware of what was happening, I decided to go through the lounge so as to not disturb them as I assumed the noises were coming from the bedroom. My roommate, a tall skinny guy and his girlfriend a tall curvy brunette art student were not too concerned about me as I am a heavy sleeper. I walked into the lounge and what I saw will be imprinted into my brain forever. She was naked on all fours on the sleeper couch and he was naked behind her with his hands on her hips giving it to her doggy style. I’m not sure how long I stood and stared for before awkwardly apologising. He looked up at me with his cock still in her and said not to worry. As I left the lounge she started giggling. They waited for me to fall asleep before continuing. Obviously I was fake snoring and very turned on. The next morning she made us coffee and all she was wearing was one of my roommates t-shirts. She went to the kitchen and my roommate whispered to me, “she wants round 2 and she wants you to watch”