The ending seems pretty clear.
Or is it? That's the trick with a lot of good short stories. They lead you in one direction and then twist things all around at the last second. You close the book thinking, "Holy crap. Did that just happen?"
So what happens in this story? Is it a straightforward ending, or is there more at stake? Let's take a look.
From a plot standpoint, the storm ends and so does the affair. It doesn't seem like anyone discovered the secret – Calixta and Alcée have their affair and seem to keep both their spouses, Bobinôt and Clarisse, from suspecting anything. The narrative ends with the line, "So the storm passed and every one was happy" (5.2). Sounds pretty neat, right? The storm and the affair are both over, all tied up in a bow.
Hmm. Well even if you haven't experienced any extramarital affairs, you've probably read about some of them. Let's see… Anna Karenina, Madame Bovary, The Awakening... We're sensing a theme here: affairs in fiction don't usually end well. So what are the chances this one has? When the storm ends, is that the end for Calixta and Alcée? Or do you think they'll try to set up another rendezvous? The story sure seems to indicate that whatever they get up to is the best thing Calixta has ever experienced. She'd only be human if she tried to recreate that pleasure later.
There's also the question of whether Bobinôt or Clarisse suspect anything. We think it's likely, judging from the text, that Bobinôt doesn't. Sure, he thinks it's kind of weird that Calixta doesn't tell him off for coming home all grimy, but that can explained by her relief that he and Bibi made it through the storm OK. But what about Clarisse? She's all too ready to take a break at the end from what she calls her "conjugal life" (5.1), which she sees as a duty. It would be easy for her to take Alcée's letter at face value – that he's doing just fine on his own – and turn a blind eye to whatever it is that's making him OK with their separation.
Regardless of whether the affair actually ends or not, or whether Clarisse and Bobinôt ever find out about it, the last word of the text is "happy." Everybody is "happy" at the end. That's what counts, right? And maybe that's why this story couldn't be published in the 1800s. (See "In a Nutshell" for more on that.)