When my wife and i were dating, we would spend some friday nights at an apoartment shared by her older sister and brother. There was always a little sexual tension between her sister and I, we almost dated the year before. One Friday night we were drinking and hanging out watching tv. My future sister in law pulled out the sleeper sofa and we were all laying on it watching tv. I was laying between the girls and my wife fell asleep. Suddenly I felt a hand on my back, her sister has slipped her hand under my shirt and was rubbing my lower back. I moaned with pleasure and moved a little to give her better access. She eventually pulled my shirt off, then hugged me from behind, i felt her bare tits on my back, she had removed her top too. I rolled over and we started making out, with my wife laying next to us asleep. She undid my pants and pulled out my cock, telling me her sister had told her i was fairly big and she had to sample for herself. She slid down and put my cock in her mouth. She gave me an awesome blow job, and then stripped naked and asked me to play with her. I licked her tits and fingered her to 2 orgasms. We got dressed and woke her sister up. I took her home, then went back and her sister and i sucked and fucked all night. She still slips me some tongue when we see each other, 30 years later.