Why does Edna get involved with Alcee Arobin?
Alcee Arobin follows Edna around and spends a great deal of time with her while Mr. Pontellier is not home. At first it is simply a friendship, Edna takes no true interest in Alcee because he love lies with Robert. She secretly always hopes for Robert, but Alcee is conveniently there. Sick of her old and rigidly-boxed life, Edna simply takes up Alcee as a lover for the companionship; she, in a sense, vicariously lives out her relationship-fantasy of Robert with Alcee.
By the time Edna leaves Grand Isle to return to New Orleans, Edna has definitely concluded that she was not meant to be Adele Ratignolle. She has fallen in love with Robert Lebrun; when he proves unavailable, she has an affair with a womanizer named Arobin. She is clearly no longer prepared to subjugate all the things she wants out of life to her husband’s ideal of the perfect marriage. She refuses to entertain the wives of his business contacts; she disrupts the routine of the entire household with her new avocation -- painting. The children are eventually taken to stay at their grandmother’s, ostensibly because "the old madame . . . wished them to know the country, with its streams, its fields, its woods, its freedom" but more likely because she realized they were being neglected by their mother. Edna moves into her own apartment, but is unable to find happiness there either, because even though she’s learned who she isn’t, she hasn’t yet learned who she is. She eventually walks into her beloved sea and drowns.
Because she doesn't get enough sexual attention from niether LEonce nor Robert..