I didn't have a sister in law, but one of my ex girlfriends had a slutty younger sister who was still 16-17 years of age. I was able then 20 years old and my girlfriend same age as me. One day, I went to her place and she decided to go to the shop to buy some groceries and make some lunch. Parents were away at work and I stayed at home with her sister. Didn't know back then how horny her sister was. I took a nap in the living room by watching TV and slightly woke up and turned to my left with half opened eye. I see the girl undressing, completely naked and changing clothes from the wardrobe and just closed my eyes and pretend I don't see anything and forced myself to ....... Some time later, I'm dreaming of some saloon where I have a massage, so pleasant, I don't remember having such a dream ever. The girl actually stroked my cock while I was asleep. When ......, usually I don't really wake up easy and engage in dreams till I feel rested. The whole thing felt so nice, until she slid her pussy on my cock. She spread one leg across the bed and one on the ground and was sliding herself on my cock like that without touching me at all. I woke up after some time and was petrified, the only thing I could do is grab her for her hips and pull her down. Couldn't hold myself and I just said "......, slow down or I'm gonna cum"! She only said "that's good!" and kept riding faster. Last thing I know is I felt hot spurts coming out of my cock inside her. Felt like nothing before: super horny and excited and terrible at the same time because of multiple reasons. That moment when you don't know how to feel while the animal side of you keeps you overwhelmed, and at the same time reason kicks in. Perhaps I did it because my girlfriend cheated on me before, sweet revenge? I will never know. Nobody will as I've never told anyone about this before 🙂