Trying to find a story and its driving me mad

Its driving me nuts, i read it a while ago and can't find it. Basically the story goes that a husband and wife make a bet that the other will want sex first. The wife ends up cheating and I believe the husband gets to have sex with other woman to be even. I think the wifes friends drove the wife to cheat to sleep with her husband. Like I said ive tried every search I could think of trying to find the story.