MC is telling his friends (a young couple that are in an open relationship/marriage) about his new wife cheating on him with his parents (IIRC). During the telling, the female of the couple, who has always hinted at wanting to have sex with him, consoles him and uses that opportunity to convince him to have sex with her. I think either his wife or female friend is named Sandy and has red hair (though that could be a memory from another story). I think there was a scene where they were doing some home repair work or painting and new wife comes out in a very sexy outfit (short shorts, crop top, braless I think).
That's all I can remember.