what do the crack up and winter dreams by f scott fitzgerald have in common

Both of these works by Fitzgerald deal with "disillusionment," the experience of seeing a false idea or belief that one has cherished over a period of time being destroyed. Though it is a frequent theme in literature, Fitzgerald deals with it in an especially striking and personal way, and there are, unsurprisingly, connections between his treatment of it in these two pieces and in his novels and other short stories.
In "Winter Dreams," Dexter is haunted by not just Judy Jones herself but the image he has created of her. He loves her but is aware of her shallowness, and yet at the end of the story when it's revealed to him that Judy has apparently lost her striking beauty and is stuck in an abusive marriage, his illusion bursts like a bubble. Judy is essentially another version of Daisy in The Great Gatsby. One can include her among people who, as Nick says of Daisy and Tom, "smashed up things," caring little about the consequences. Like Gatsby, Dexter is a social climber, a man from (like Fitzgerald himself) a middle-class, northern Midwestern background who aspires to join the upper crust of society. Dexter becomes a success in business but feels incomplete, even with his engagement to the obviously right-for-him Irene. When he falls for Judy again, he torpedoes, without any real regret, his engagement to Irene and the spiritual comfort it might have given him.
"The Crack-up" deals with the exploding of an illusion, but on a deeper, more transcendent level. Fitzgerald recounts in honest detail the mid-life crisis he experiences after fifteen years as a successful writer. (Eighty years ago, people who were thirty-nine years old did actually think of themselves as being in the "middle" of life.) It is a spiritual self-reckoning compounded by the external changes in the artistic world of the time, in which film is becoming the dominant art form and replacing Fitzgerald's craft, writing. Fitzgerald gives the impression, like Dexter, of having lived in a dream world that collapses when he comes face to face with a new reality. And yet, unlike in "Winter Dreams" where the reality is the end of one's obsession with a woman, Fitzgerald never gives a single, definite explanation of why the crack-up occurs. In all his descriptions, however, there are two statements which to me stand out above the others: "I saw that for a long time I had not liked people and things, but only followed the rickety old pretense of liking;" and "...in a real dark night of the soul it is always three o'clock in the morning, day after day." This is a man confronting an existential dilemma. The incidental things that Fitzgerald mentions as contributing to the crack-up: the exhaustion, the concerns about his health, his annoyance with the trivialities of the world surrounding him like the sound of the radio and the advertisements in the magazines, and the backfiring advice of the woman in his life—these are all symptoms of a more fundamental feeling of insufficiency, of emptiness at the core of a man's life. It's tragic that after writing "The Crack-up" Fitzgerald had only a few short years to live and not enough time to overcome this feeling.
In both "Winter Dreams" and "The Crack-up," dealing as they do with the collapse of illusion, Fitzgerald leaves open the answer to the usual problem of "the meaning of life." In these works, as in his "The Curious Case of Benjamin Button," where a man lives his life backward from old age to the cradle, we are left, after considering the details of each story, with the question, "what was the point of it all?"—apart from the basic fact that life is what it is.