From about 1992 or so:
In my first marriage we played around a bit, threesomes with another girl then another guy, dates with people we wanted to fuck. While the marriage did not last the sexual adventures were not a reason for the breakup.
Some years later, in my late forties I remarried a girl eleven years my junior. She was 5'6, blond hair, 115 pounds with 36C breasts. She had been in San Francisco for the Summer of Love and was very sexual. While I had made love to a dozen women she had racked up over fifty lovers. We had sex on the first date and almost every night for the next year or so.
Then years of smoking and high cholesterol started slowing down my responses to the point that an erection became an unusual event. We still had sex. She did not climax often from intercourse so I would end up eating her to a finish. I could tell though that she missed my cock.
We were into role playing, going out on dates with each other or meeting in bars with me picking her up. One day I brought up the possibility of her taking on a lover for regular intercourse. Over the next several months we continued the dialog and she slowly came around to seeing the possibilities of this type of arrangement. She admitted that she would enjoy having regular sex once or twice a week. I told her that I would love to watch her at least once and we agreed to consider that.
She started looking for someone who could fit that role. She did not want to do a married man but was more than happy to consider someone single. Finally, she told me about Tim. He worked with her, was single, her age, the body type she liked and had sometimes seemed friendlier than a co-worker.
One day she wore a short skirt and tight blouse and invited him out for a drink after work. The drink led to a visit to his house, to see some work he had done on an old car. He offered her another drink, then had her look out the window at the car. He came up behind her, grabbed her tits and stuck his hard cock into her ass. Clothes came off and he fucked her on the spot.
While his cock was about the same length and diameter as my five and a half inch one, the head was as big as a plum. She said when he stuck it into her the first time she came on the spot. He fucked her very fast and came almost at once. Realizing that she had not told me she was going to be late she dressed and left after agreeing to visit again on the weekend.
You can imagine my excitement when she came home dripping cum. I actually got a large erection and we fucked several times with me adding to the cum in her. She was very excited about Tim and was sure this was what we were looking for. I loved what it did to both of us.
A couple of days later she came home from work, gave me a big wet kiss and I immediately noticed the musky scent of cum on her breath. As she was ready to leave work Tim had pulled her into a darkened office and pushed to her knees while bringing out his hard cock. I had told her earlier that the best way to nail a man was to give him a blow job and swallow his cum. That's what she did.
The weekend came and she was all excited about her date for Friday night. She selected a short black dress, no bra or panties. She left and I experienced that feeling that I had known before. A cross between fear and sexual excitement. Several hours later she came home but I could see that she was crestfallen.
When she got to his house he had stripped her dress off. She immediately blew him hoping to slow him down. After he came she continued sucking his cock until it came back up at which point he pushed her to the floor and fucked her hard and fast. He came again but she did not. While they had a drink she talked to him about slowing down and he promised to. He was all excited about having her as a regular fuck and even wanted to perform in front of me. She went down on him again and got him hard, this time he got her on all fours and entered her from behind, her favorite position. But as soon as he was in he pumped as fast as he could and came again in just minutes. As she was laying on the floor she saw a face in the window. It turns out he had told his cousin about this hot married woman that wanted a fuck partner and let the cousin watch. He told her his cousin had a big cock and from time to time they would share women, that maybe they could do her.
While he was not the best lover, he still got hard at the sight of her body so she wanted to keep going with him. She knew I wanted to watch her get fucked by Tim and she kind of wanted that also thinking that maybe the sight of it would help solve my problem. Tim agreed to come over in a couple of days but kept putting it off until she realized he was not going to do it. At that point she dumped him.
That kind of killed her interest in taking lovers at least for a long time.