Why does Edna get involved with Alce 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.