In one brief scene in Chapter VII, after Myrtle's death, Fitzgerald captures the essence of Tom and Daisy's relationship:
Daisy and Tom were sitting opposite each other at the kitchen table with a plate of cold fried chicken between them and two bottles of ale. He was talking intently across the table at her and in his earnestness his hand had fallen upon and covered her own. Once in a while she looked up at him and nodded in agreement.
They weren't happy, and neither of them had touched the chicken or the ale--and yet they weren't unhppy either. There was an unmistakable air of natural intimacy about the picture and anybody would have said that they were conspiring together.
There is a natural intimacy between Tom and Daisy, but it is not merely the intimacy of marriage. It is the intimacy between two people who share a common background and common values (or lack of them) and who move in the same wealthy world, know the same wealthy people, and observe the same superficial social conventions. Tom and Daisy are united more by their social class and its mores than by marriage. Nick observed:
They were careless people, Tom and Daisy--they smashed up things and creatures and then retreated back into their money or their vast carelessness or whatever it was that kept them together . . . .
What keeps the Buchanans together is that they are just alike. Both are amoral beings, users united by their mutual sense of entitlement. Both are far too selfish to love.
Daisy's emotional state at the conclusion of the novel? Surely shaken by events and frightened that she might have to assume some responsibility for her own actions, she retreats into the familiar and hides behind Tom and his money. They do conspire together in their kitchen while Gatsby, in great irony, stands watch outside to protect her. They will simply run away and leave it to others to "clean up the mess they had made."
At the end of the novel, it seems that Daisy's emotional state seems to be one cloistered within the superficial, yet protective enclave of class and wealth. There seems to be an emotional void in Daisy's life. She seems to be rather neglectful as a mom, and unwilling to stake an emotional connection to anyone in her life. Her marriage to Tom is predicated on social standing and the protection of "old money." The materialism and consumerism of the age, along with the emerging fascination with celebrity, all seem to converge within the character of Daisy. Her depiction in the novel does not seem to present her with a valid and noble emotional lineage. At best, she is emotionally fragile, unable to accept her responsibility for driving the car that killed Myrtle, unable to commit to Gatsby, who demonstrates more love and affection for her than her husband. At worst, she is unwilling to take a chance with Gatsby and sacrifice her social standing and will not risk the discomfort with accepting responsibility when "someone else will take care of it." Her emotional state can either be seen as manipulative or crippling, dependent on how one sees it.
This renders a vision of a marriage that is hollow, at best. Her relationship with Tom will sustain because both are more concerned with the veneer of appearance, the illusion of happiness, than actually working towards its actualization. He will continue to disrespect her and she will continue to live the life that is accustomed to someone of the upper class. Fitzgerald creates the predicament where the wealthy live for the implications of their wealth. His portrait of their marriage is one based on convenience, calculation, and a certain level of objectification, where they and their marriage are objectified by their wealth, as opposed to active agents who are in control of it.