I think the central way that this question can be answered is through an examination of the character of Robert Lebrun. He is clearly the instigator in many ways of Edna's awakening, and although he spends the majority of the novel away in Mexico, his presence is tangible throughout the whole novel. However, crucially, he, unlike Edna, shows that although he flirts with different roles, he is very much bound by society and the roles that society gives him. Edna rejects the roles of mother and wife imposed upon her, but Robert is unable to act in a similar way. Indeed, his inability to do this is what causes him to desert Edna at the end of the novel, as he realises that society will make it impossible for him to act on his love for Edna. The final note that he leaves her, with its message, "Goodbye--because I love you, goodbye," indicates clearly the way in which Robert has realised he truly loves Edna, and therefore is leaving her as a result, because society will not allow him to consummate their relationship.
Just as Edna experiences an epiphany about how society restricts her, so Robert Lebrun undergoes a similar epiphany in which he understands how much his desires are curtailed by social norms and conventions. The difference is that Edna chooses to defy society, whereas Robert opts to stay well within its confines.