We're often taught that cheating is wrong – on a test, in a marriage, whatever. We think of it as being dishonest, or as a kind of sin. "The Storm" is not so black and white, though. Yes, Calixta and Alcée cheat on their spouses by having an affair and act as if nothing happened, but afterwards they seem to be kinder and sweeter to their spouses. Their hypocrisy seems to help strengthen their marriages rather than destroying them.
Because neither Calixta nor Alcée reveal their affair to their respective spouses, no damage is done to either of their marriages. It's as if the affair had never happened.
Even though Calixta and Alcée cheat, the act of cheating makes them kinder to each of their spouses. In this way, everyone benefits from what might otherwise be considered a sin.
While everyone seems "happy" at the end of "The Storm," the affair and its aftermath reveals the deep-rooted problems in the marriages of both couples.