It's a long story, so I'll try my best to condense it as much as possible.
Much like another poster as already said, long before the internet, Penthouse magazine published monthly Reader's Digest sized magazines called Penthouse Forum and Penthouse Variations, supposedly letters written by readers (although most stories seemed to be written very professionally). 😉
The stories that seemed to turn me on most were about cheating wives, shared wives, and voyeurism.
My wife and were high school sweethearts, and married after our first year of college. I was her first and only sexual partner, and the idea of her having sex with someone else was somewhat scary, but also very erotic and exciting!
Eventually I told her about these stories, and I shared that I had fantasies about her with other men. At first she said that wasn't going to happen (she was raised very conservatively), but as we were approaching that marriage cliché the seven year itch, she admitted she had started wondering what she might have missed by not playing the field a bit before we married. Her younger sister went through a lot of men before she settled down, and I think my wife was envious of her experiences.
After a lot of talking, we agreed that she should try having sex with someone else, but she was adamant that it had to be someone she felt safe with, and someone she liked and knew well enough to get intimate with.
Shortly after that, a close friend of ours caught his wife cheating on him, and they went through a very nasty and drawn out divorce. He lived in another city at the time, but my wife and I spent many hours during that time talking to him on the phone, helping him get though it, and lending a sympathetic ear.
Once the dust had settled and he was single again, he asked us if he could come out for an extended weekend. He needed to get way, and he wanted to spend some time with friends! He also wanted to thank us in person for helping him during a rough time. We of couse said yes, and he made plans to come up the next weekend.
It wasn't until after we got off the phone with him, that I noticed my wife seemed lost in thought. When I asked her what was on her mind, she got this playful grin on her face and said "Gino's been through a lot, and his confidence with women is obviously pretty damaged after his divorce, and I was just thinking, I could help him with that confidence, and he could be the first guy other than you to ...... with me! What do you think?" I was shocked at first, but then had to admit I knew she had always found him attractive, and he was clearly crazy about her! She was right, he would be the perfect choice, so I told her she should go for it.
She did, seducing him on the dance floor the second night of his visit, while we were out clubbing, and then coming back to our table and having me tell him she was his for the night! He didn't believe us until she leaned over and kissed him passionately right there in the bar. We quckly settled the check and head home, where she promptly led him upstairs to our bedroom where he fucked her twice! That was the first of many meetings between them, and the start of our journey in this lifestyle. She was 28 when that happened, and she recently turned 59, so we've been doing this for over 30 years!