I believe it was one where there was a "her point of view" and a "his point of view".
Husband/wife made wager with each other, wife is somewhat competitive about it, and wife ends up sitting on her living room couch with two much younger men, husband just ups and announces he's going to bed, and listens to what transpires through a monitor or something. Naturally, the somewhat hesitant wife has sex with the two young men.
Very well written story, can't find it.
Thank you in advance.