Looking for a specific story.

From what i remember, the main character is a guy who is married. The story is about how one of his friends blackmail him and his wife into having sex with the other's significant others, the wife is to have sex with the friend and the mc is supposed to have sex with the blackmailer's wife and both the ultimate goal is to pretty much train both to be obedient to the blackmailer. The husband is disgusted but goes along with it until the allotted time is up, but the wife ultimately breaks and sides with the blackmailer guy after time is up. This takes place over a few weeks to months I believe. At some point, they even try therapy but the blackmailer kinda hijacks it to paint a picture of a polygamous relationship gone wrong and the husband walks out.