I rmr watching this movie around 2001. It about this couple that go on a vacation, maybe, to this beach. They meet this other couple. After drinking they decide to swap wife's. Later one of the guys see the girl from the other couple having fun with a cop, so he goes to save his wife that's is with the other guy. I rmr the end scene where there is a guy with his dog on rooftop reading the letter where this story was written.