William Doherty in Fitzgerald.narod.ru:
Critics often express a feeling that there is something mysterious about Fitzgerald’s Tender Is The Night, that there is something unsatisfying in the analyses we have had—a discomfort one does not feel with the more elaborately structured The Great Gatsby, or with the intriguing, unfinished The Last Tycoon. Searching the critical opinion on Tender Is The Night—this “magnificent failure” —one is likely to feel that something is missing; one seems to have, as Maxwell Geismar says, “the curious impression at times that the novel is really about something else altogether.”(Maxwell Geismar, The Last of the Provincial, (Cambridge, Mass.. 1947), 333.) It seems strange that the relationship between the novel and Keats’s “Ode to a Nightingale,” which supplied Fitzgerald with both title and epigraph, should have received no more than passing attention from the critics. The epigraph reads:
Already with thee! tender is the night,
…
But here there is no light,
Save what from heaven is with the breezes blown
Through verdurous glooms and winding mossy ways.
We know that Fitzgerald had a lifelong and deep response to Keats: “for awhile after you quit Keats all other poetry seems to be only whistling or humming.” The “Ode to a Nightingale” was especially important to him; he found it unbearably beautiful, confessed he read it always with tears in his eyes (F. Scott Fitzgerald, The Crack-up (New York, 1956), 298.)It is true that the title Tender Is The Night was chosen late in the extended course of the book’s writing; but it seems clear that Fitzgerald was conscious of the “Ode” not merely in the last stages of composition. The title is appropriate, though no one has said why. Yet, a moment’s reflection will show that there is a good deal of Keatsian suggestiveness in Tender Is The Night in both decor and atmosphere—the Provencal summers of sunburnt mirth, the nights perfumed and promising, the dark gardens of an illusory world. But I suggest that there are parallels more significant than those of color and mood. The correspondences I offer in this case, when taken individually, might seem no more than coincidental; but considered in their cumulative weight, they indicate a calculated pattern of allusion beneath the literal surface of the novel which deepens the psychoanalytic rationale and adds context to the cultural analysis the book offers. In addition, the “Ode” appears to provide us with a sort of thematic overlay which clarifies unsuspected symbolic structures, essential to the understanding of the book.
More here. (Note: Just re-read Tender is the Night and was deeply moved all over again by its beauty and sadness.)