How do Dexter's dreams reflect his discontent, and does this feeling subside when he fulfills his ambition to become rich?
Dexter's dreams include wanting to be, or feel, equal to the wealthy members of the Sherry Island Golf Club for whom he caddies, going to an exclusive university in the East, and achieving great wealth. To his credit, he realizes all of his "winter dreams." However, when he finally joins the men he once admired, particularly T.A. Hedrick, whom he had fantasized about defeating in a game of golf (he did not specifically want to become a golfer), he finds the experience underwhelming and does not think that Hedrick is such a great golfer but perceives him as a "boor."
He becomes rich, but still does not win Judy Jones, the girl from his town with whom he had fallen in love. He idealized Judy, which made it harder to accept his associate Devlin's news that she aged and had an unhappy marriage in Detroit. Dexter is also shocked by Devlin's assessment of Judy's looks—"pretty" when she was young, with "nice eyes"—because Dexter had always perceived her as "a great beauty."
Dexter's "winter dreams" are Fitzgerald's metaphor for the American Dream which relies on a never-ending pursuit for happiness. The pursuit is never-ending because someone like Dexter is never quite content with what he has accomplished and obtained, but always longs for the thing he could never have—in this case, Judy.
When he realizes that he "can never go back"—that is, never return to his hometown of Black Bear, Minnesota and resume his on-again, off-again relationship with Judy because she is not what she once was—he feels a sense of loss that makes everything in his life matter less.
Dexter dreams of becoming a famous golfer and playing golf against those for whom he caddies now. By playing against them - and beating them - he sees the fulfillment of his deram. He will be successful.
His sense of deprivation does not subside when he becomes wealthy because there is always something more. A wonderful young woman, for instance, becomes engaged to him, but he breaks it off to pursue Judy - a wealthy young woman who he had met in the past. He is unable to enjoy his success because he always feels he has something else to prove and wants more.
Even when Judy proves to be shallow and selfish, Dexter is unable to break with his imagined vision of her until the very end when he is told that Judy has become a housewife married to an alcoholic husband and is no longer the beauty she once was. This becomes a reality check for Dexter who realizes that there really is no stability in the dream he has chosen to pursue.