Looking for story where a wife cheats with a stranger, and then hires stranger to captain a boat with her and her husband?

[HappilyDepressed]

Basically the wife (and a friend) have a weekend where they hook up with two strangers (who I believe were…South American?), and one way or another, the wife ends up on a boat with her husband and both gentlemen. They’re manning the boat, I forget what the intent is. They agree to keep quiet about the affair, one of the men takes her necklace and they have sex in order for her to get it back. Last time I read it, it left off on a cliffhanger where the wife was to be left on the boat with the other guy.