After Arobin leaves her, Edna is overwhelmed by various emotions. She feels alternately sad, irresponsible, and shocked at what she has done. Surrounded by the material possessions that her husband has provided for her, she feels a little guilty, but the strongest reproach comes from Robert, whom she really loves. Mostly, she feels like the experience has allowed her to see and understand the world more clearly. Although she has no shame or remorse, she does regret that she slept with someone because of lust, rather than love.
Why does Edna sleep with Arobin if she's really in love with Robert? The narrator does not offer any definitive explanation, and there's really no need for one. Edna sleeps with Arobin because she desires him at that moment, and she simply acts on her impulse. She does not feel particularly disloyal to Robert or to her husband because she considers herself a free woman, able to sleep with whomever she chooses. She feels slightly guilty towards her husband only because she is still living in his house, and she feels regret because Robert had not gotten there first before Arobin. In short, the negative feelings surrounding her first experience of adultery concern more the specific circumstances of the affair, rather than the larger question of disloyalty.
After sleeping with Arobin, Edna feels an increased sense of understanding. She has learned what it is to act completely in the moment, without regard to consequence, and she now knows what it means to use her body for purposes of pleasure. She has broken the paramount rule of marriage and has crossed outside the realm of social respectability. From this vantage point, she can see the rules of society for what they are: just rules, and rules that can therefore be broken.
Without deliberating about it, Edna immediately sets about moving out of the big house on Esplanade Street. She wants to escape from her husband's possessions which surround her, and she sends her own things over to the smaller "pigeon house." Arobin finds her standing on a ladder, looking healthy and vigorous, unhooking pictures from the wall. If he's surprised by her behavior, he doesn't show it and after unsuccessfully trying to get her to get off the ladder, helps her in her task. Like Edna, he wears a dust-cap, which the maid Ellen finds hilariously funny.
Edna does not want to be alone with Arobin, and they converse a little about the elaborate dinner party she will throw in two days to celebrate her departure. After the dinner, Edna will completely move into the "pigeon house." Excusing herself to finish her chores, she tells Arobin that she will see him at the dinner, but no sooner. Arobin protests a bit, but looking into her eyes, resolves to wait until then.
As has become her habit, Edna decides to move out of her house without carefully considering her actions and fails to even consult her husband. She acts on impulse, knowing that she cannot continue an affair while still living in her husband's house. As she sees it, it would be grossly hypocritical of her to continue living as one of his possessions while treating her body and her person as her own.
Edna shows an almost surprising lack of emotion towards Arobin. Her attitude is almost completely neutral, and she exhibits neither the sexual attraction nor the awkwardness that one might expect. However, her relative indifference does make sense. She is not particularly attached to Arobin, and their affair was simply the result of a momentary whim. She didn't spend that much thought going into it, so there's no reason why she should analyze it afterwards. Similarly, she makes no promises about whether or not it'll happen again: if it does, it does; if it doesn't, she wouldn't really care that much either.
The fact that Edna and Arobin spend their morning-after cleaning her house has symbolic importance. Just as Edna is removing old fixtures from the wall and dislodging dust everywhere, so is she ripping away whatever prejudices, ties to convention, and entrenched social privilege she may have previously had. She is forging a new life path for herself, but before she can do so, she must first get rid of the relicsthe old attitudesof her past.
Edna's special dinner is actually a small, intimate gathering of people, due to Madame Ratignolle's advanced pregnancy and Madame Lebrun's last-minute no. The guests present are Mrs. Highcamp, Alcée Arobin, Mademoiselle Reisz, Monsieur Ratignolle, Victor Lebrun, an intellectual young woman named Miss Mayblunt, and her bland companion Gouvernail. They all sit around an elaborately and expensively decorated table, and wearing new diamond jewelry from her husband, Edna admits that it's her twenty-ninth birthday. They then proceed to drink the Colonel's health with one of his invented cocktails.
Wearing a golden satin gown, Edna sits regally among her guests, who chat pleasantly with each other. Though they are having a good time, she feels overcome with boredom and despair. She is filled with longing for Robert, yet simultaneously feels that he is unattainable. The guests continue to laugh and have a good time, until both Monsieur Ratignolle and Mademoiselle Reisz get up to leave. As Edna escorts them out the door, Madmoiselle Reisz slyly tells her to be good.
When she rejoins the rest of her guests, she finds Mrs. Highcamp weaving a garland of roses for Victor, who then poses with a white scarf draped around his neck. The color contrasts are striking, and Victor looks exotic and extremely handsome. When asked to sing, he looks at Edna and starts to croon "Ah! si tu savais!," the song that she associates with Robert. Edna reacts violently, demanding that he stop and accidentally shattering a wine glass on the table. He apologizes gently to Mrs. Pontellier and kisses her hand, and pulling the garland and scarf away from his head, she tells him to stop performing for them. At this point, the rest of the guests depart and enter the quiet, still street.
This chapter is very similar to the climactic scene of Virginia Woolf's Mrs. Dalloway, in which the title character successfully draws together various guests for an elaborate little dinner party. Like Mrs. Dalloway, Edna feels removed from the pleasant chatter of her guests and doesn't actually enjoy the occasion. She has created the illusion of intimacy among her guests, but she does not participate in the illusion. The dinner party is like one of her paintings: although aesthetically pleasing, it is just the picture of reality, not reality itself.
The dinner table is perfectly decorated, and Edna herself looks majestic and gorgeous in her gown. Her guests talk constantly, but as the description of their conversation implies, they don't really say anything of substance. They are there to celebrate Edna's departure from the conventionality of high society, but ironically, they are all members of the social elite. They do not really understand why Edna is leaving Esplanade Street, and so their interactions, though pleasant and very agreeable, are exactly the kind that Edna is trying to escape: formal, prescribed, and embedded within a specific social context. Feeling bored, Edna longs for something indescribable, but which is the sincere, emotional bond that she has with Robert.
When Victor poses for the gathering, he creates a different kind of picture, but one that is equally false. He becomes a stand-in for Robert when he starts to sing "Ah! si tu savais!", but as Edna knows all too well, he is not his brother. He evokes the specter of Robert, but the illusion that he creates is inevitably false.