We are an older couple, married 30 years - 2nd marriage for both of us. Long story short (I'll share the details in another thread): my wife's boss was her lover for roughly 9 years. He became her primary sex partner, but I wasn't complaining as the sex I did have with her was off the charts hot as well. My wife knew how to exploit the situation to gain total commitment and arousal from me. Her boss's wife was in a wheelchair and there was no sex between them so he was horny all the time. And there was my wife, - right outside his office. In a way, my wife Linda became his "wife" and Linda traveled with him as his wife on some occasions. He was the president of the company and so traveled all over the US and several times a year to Canada where the company's manufacturing was based.
Linda was the executive secretary, and her first sex with him (that I know about) was on the couch in the corporate office after work one night. The company maintained a hotel room nearby for visiting executives and Linda and her boss would often go there to have sex, sometimes spending the night. It was always "first cabin" - nice dinners, nice hotel rooms, and when they traveled to business events they had separate rooms but Linda stayed with him in his room. She was in love with him, but when I expressed my concern at the high level of emotional involvement, Linda assured me that our marraige was indeed safe, - that she "could love two men" and would always love me.
It wasn't long before we had our first pregnancy scare. I've had a vasectomy so there's no chance I'm the dad if she is PG. It forced us to discuss this and be serious about it - not just fantasy talk. We found we liked the idea, but knew we needed to proceed VERY carefully. The thing is, once your wife has a couple of late periods, you're forced to decide what path you want the relationship to take over the long term. I'll probably tell about that in another post as this one is already too wordy.
Linda also enjoyed several weekends and couple of three day weekends with different lovers - in a hotel at a local resort area. My wife prefers overnight fun, and needs to have some interest in or feelings for any lover for him to get an invitation for a repeat perfoemance. We've always preferred coworkers from her workplace - guys she knows before considering going to bed with them. It helps screen out duds and conversation flows much easier with a guy she has workplace experience in common with. Helps "break the ice" as there's shared experiences.