My wife (of 30 years) had a long term lover early in our marriage. Probably started 5 years after we married. We'd had a few erotic threesomes with other guys before and were not inexperienced, although we weren't balls out swingers either. We'd never heard the terms "cuckold" or "hotwife" before, but we knew we liked her having extra males from time to time. Still, we had never discussed the implications of her "falling in love"l with another guy.
My wife was very attracted to a certain male coworker. Their work travel schedules often put them in the same out of town locations for overnights. She'd told me she found him attractive and if the opportunity arose........ naturally, I encouraged her. One night after a small party in our home, everyone had left except him. I'd already gone to bed (the alcohol was doing its work on me). My wife and Paul began making out downstairs in the living room and soon after she took him to the guest bedroom and went to bed with him. I'll skip the rest of the more lurid details, pregnancy scares, etc. but that's how it started.
They became a regular item and our sex lives were supercharged, it was good for all three of us. One morning after he left (they'd slept together in our guest bedroom, same as always, he was not comfortable with me in bed with them) my wife shared with me that she had feelings for him and wanted to be honest with me about it (as if I didn't know!). She said she would break it off if it presented a threat to our own relationship. I asked her if she could deal with it. "I can love two men," she said, "and I only want to be married to you. I think I love Paul as well, and I certainly love sex with him," she said, almost in tears. I reassured her that I was good with the situation as long as it didn't negatively impact our marriage and we agreed to be sure and communicate with one another if we were insecure, saw threats, and so on. Selfishly, I really wanted it to continue as our marital sex since their relationship started was just over the top good! We both agreed that was the case.
This relationship lasted about five years. It only ended because Paul's wife became insecure and jealous. None of us wanted negative impacts on our marriages, so my wife and Paul broke it off. The end of it was not without tears, but we all lived through it. Paul's marriage survived as well, and he and my wife had one reunion about 3 years later, - a weekend in a luxury resort. While they enjoyed the weekend together, it was painful for them in a way. That was well over 20 years ago.