I had this experience only once a long time ago. I had become casual friends with a guy at work. We would occasionally go out for drink after work. My spouse always got home from work later than me. So a drink or 2 was just a time killer till I went home for dinner. One day, I’ll call him Bill, said if you are up for a post work cocktail how about coming over to the house. I said sure. He lived on my way home so it wouldn’t be out of my way. I follow him home. He makes us each a drink and we relax watching the local news. This was the first time I had met his wife who was in the kitchen doing some pre dinner prep. Not long after we sat down she also made herself a drink and joined us just hanging out. They appeared to be the perfect middle aged couple. Both in great shape. And no kids by choice. I finished my drink. Thanked both of them and went home. About a month later Bill had his car in the shop. His wife had dropped him off in the morning and he asked if I could give him a ride home and join him and Ann, his wife, for a drink. I said sure. On the ride to his house he mentioned how Ann had enjoyed meeting me. Then he startled me by asking if I was familiar with the term spitroast in the context of a sexual act. I told him that I knew what it was and had seen it in porno vidieos. I started laughing and asked him why he would bring something like that up. He got real serious and said that Ann had always wanted to try it and specifically asked if you might try it out with us. Even though I thought he has to be kidding, I readily agreed to help Ann fulfill her fantasy. She greeted us at the door. She got us all a drink and we just sat down in their living room. I was too afraid to say anything about what Bill had mentioned in the car. But Bill, with a big smile, announced to Ann that I was willing to do a spitroast with them. Ann said great. Let’s finish our drinks and try it out. At this point I asked Ann to be tell me exactly what roll she wanted me to play. She said that she wanted me to fuck her doggy while she sucked Bill’s cock. I still thought they were kidding, but readily agreed. With our drinks finished, she came over to where I was sitting and knelt in front of me. She effortlessly unzipped me, took out my cock and started sucking it. In short order we were all naked. Ann led me into their bedroom. She got on her knees and waited for me to enter. She felt great. After I had a rhythm going, Bill knelt down in front of her and positioned himself so Ann could easily take him into her mouth. It took just a few minutes for Bill to explode into her mouth. By this time I had adjusted to the shock of fucking a guy’s wife right in front of him. I firmly grasped Ann’s hips and was ready to get serious. In short order I filled her with a huge load. We all collapsed in exhaustion. I said that I had to run. Got dressed and went home. I still remained friends with Bill but never again went to his house. It was just a fantasy for him and his wife to try once.
And non-monogamy isn’t cheating. And saying “you’ll cheat on each other” is not friendly.