perform what society has deemed as their duties toward their families. Leonce is considered a model husband by the other women in the Pontellier's social circle; however, we see very little interaction between Leonce and Edna. Early in the novel, when the family is vacationing on Grand Isle, Leonce goes to the club for dinner only to return much later to chastize Edna for not attending to one of their "sick" children. He has not spend the evening with the family and accepts no responsibility for the children's care. He wakes Edna to scold her and to insist that she do something. This could be considered antagonistic behavior, but Edna herself thinks that it is unusual for her to cry or have any emotional reaction at all, as scenes such as these "were not uncommon in her married life." She recognizes that "They seemed never before to have weighed much against the abundance of her husband's kindness and a uniform devotion which had come to be tacit and self-understood." While over the course of the novel, Edna and Leonce do argue as Leonce attempts to tighten his hold over his wife, who begins to act out and behave erratically (such as when she leaves the house in New Orleans when she is supposed to be waiting on callers), it is clear that Chopin does not want to paint Leonce as a particularly villainous individual or even as a bad husband; he's simply the typical husband of the time. The problem is with the institution of marriage and the social mores that govern women's behavior, not with this one man who seeks to uphold the gender norms of the society in which he was reared. While Robert is younger and seemingly more carefree, when it comes time for Edna and Robert to confess their feelings for one another, Edna is shocked to hear that he wants to make her his wife. Over the course of her awakening, Edna has come to realize that she feels oppressed  by marriage -- as an institution --(note how she reacts to her sister's wedding) -- and even though she loves Robert, she does not want to "belong" to any other person.

That said, if there is an antagonist in the form of a person, it may be Edna herself. She struggles throughout the novel to understand and to articulate the feelings she has toward her position "in the universe," as the narrator notes early on. She is torn between the side of her that has been brought up to believe in strict gender roles and propriety and the newly-awakened side of her that wants to simply act and be as she sees fit (this is Emersonian -- she does not feel the need to be consistent and acts on whims and impulses and does not apologize for it). Edna realizes that she has always understood that she, and by extension, other women, live different lives on the surface than what is true to their selves under those socially-appropriate surfaces. However, it is only during the course of the novella that her rebellious side begins to act out and to defy the conventions of her time and her society. Eventually, Edna's decision to drown herself could be seen as her inability to resolve these two conflicting internal voices or forces. 

If you see Edna as the protagonist and her attempts to define herself independently of husband and children as the mian conflict, it would make sense to me to call her husband, Léonce Pontellier, the antagonist.

For me, one of the most telling scenes in the novel that shows this relationship is in chapter one, summarized in the enotes study guide as follows:

Leonce lights up a cigar and sees his wife Edna walking up to the cottage with Robert Lebrun. He reprimands them for bathing in the heat, and gives back her wedding rings, which she had taken off prior to going to the beach.

Léonce is certainly the one with whom Edna has muted and open conflict, and this conflict shapes pretty much the whole story.

Of course, even a short novel is a novel, with many characters and plot lines. There may not be a single antagonist in The Awakening.

The true antagonist that stands in the way of Edna Pontellier's bid for independence and her quest to discover herself and fashion her own identity as she wills it to be is society and the way that it is shown to have created such a restricted and hemmed in position for women, especially women who are married, have children and are of a certain station. The whole book charts Edna's growing realisation that she is deeply unhappy with her life and that she wants more than she has been allowed to have. From when she begins to question why she obeys her husband so complicitly early on in the book she feels encouraged to imagine a different kind of life that she is able to live independently from him, from her children, and from society itself. Note how this is explored when she moves house to a residence that is much smaller:

There was with her a feeling of having descended in the social scale, with a corresponding sense of having risen in the spiritual. Every step which she took toward relieving herself from obligations added to her strength and expansion as an individual. She began to look with her own eyes; to see and to apprehend the deeper undercurrents of life. No longer was she content to “feed upon opinion” when her own soul had invited her.

Edna is therefore able to develop her own identity and sense of self through moving residence, and in particular through moving to a smaller location where she is not able to host the dinner parties and entertaining expected of a woman of her station in society. This is something Edna finds intensely liberating. However, as the novel shows, at every stage in her quest for self, Edna is opposed by various forces of society. Whether these forces are in the guise of her husband or friends or other individuals, or even Robert himself, Edna quickly realises that society has won, and that she has "swam out to far," to use the metaphor that the book itself uses to describe how she has overreached herself. Her eventual suicide is a recognition that the restricting forces of society have actually won.

In Kate Chopin’s novel The Awakening, various characters might be considered antagonists, including the following:

• Edna Pontellier becomes increasingly antagonistic toward her husband, Léonce. Léonce, it is true, antagonizes Edna in one of the early chapters of the book, when he returns home from a night of drinking and gambling and accuses her of paying insufficient attention to the children. He also antagonizes her later when, back in New Orleans, he accuses her of paying insufficient attention to her social responsibilities.  As the book develops, however, Edna becomes increasingly distant from, and antagonistic toward, her husband, as when she moves out of their home and also when she engages in romantic affairs with two other men.
• Those two other men – Robert Lebrun and Alcée Arobin, also have antagonistic feelings toward one another.  Robert, in particular, dislikes the free-wheeling, amoral, indeed even immoral Alcée. Robert distrusts Alcée’s interest in Edna
• Ironically, for part of the novel, Edna is in a somewhat antagonistic relationship with Robert, the man she thinks she truly loves. When Robert realizes that his relationship with Edna is becoming too serious, he leaves the immediate vicinity and goes to Mexico. This sudden decision on his part annoys and vexes Edna.
• As Edna’s friend, Adèle Ratignolle, begins to realize that Edna is growing too fond of Robert and that Edna later has begun an affair with Arobin, Adèle becomes a kind of friendly antagonist toward Edna.  It is largely because of warnings from Adèle that Robert decides to leave Edna, and it is Adèle who later warns Edna that she risks both her reputation and her relationship with her husband and children (especially the latter) if Edna continues her relationship with Arobin.
• Edna’s relationship with her visiting father, the Colonel, is not especially close, and although she gets along with him better than she had expected, he is an antagonist in the sense that he advises Léonce on her to handle women with proper masculine control.
• Ultimately, Edna comes to regard even her children as antagonists who may enslave her:

The children appeared before her like antagonists who had overcome her; who had overpowered and sought to drag her into the soul's slavery for the rest of her days. But she knew a way to elude them.

• However, her larger antagonist (it might be said) is the social system of her period, which has helped dictate her marriage and the nature of her marriage and which is at the root of much of her sense of being constrained and unfree.