Much like F. Scott Fitzgerald himself, Dexter maintains the perception of the rich as possessing some magical quality; thus, he is easily motivated to fall in love with Judy in order to experience such magic.
When he first sees Judy at age fourteen, she is a younger girl, and he notices the "passionate quality of her eyes." Her smile, too. arrests him: it is "radiant, blatantly, artificial--convincing." Later on, Dexter describes this smile to himself as "preposterous." In a way Judy is Dexter's muse; that is, she inspires Dexter to become rich so that he can have a chance with her.
However, because Dexter's vision of Judy is unrealistic, serving only to inspire his own fantasies, his "winter dreams" become illusory and fated as he is "unconsciously dictated to by his winter dreams." While he does attain wealth, the magical quality is lacking, and Dexter is disappointed in his renewed relationship to Judy after he abandons Irene. For, she is
...entertained only by the gratification of her desires and by the direct exercise of her own charm.
Yet, tenaciously Dexter holds his dreams of Judy, and it is only when he learns years later of Judy's loss of beauty and her mistreatment by her husband, that Dexter sadly realizes that she, too, is made of clay. "The dream was gone. Something had been taken from him" when Dexter hears of Judy's mundane life that lacks any animation. Dexter has lost his "winter dreams."