Careless People: Murder, Mayhem, and the Invention of the Great Gatsby by Sarah Churchwell:
While Scott consorted with the New York ghosts who haunted him, Zelda concentrated on the present. Alone with his manuscript over the phantom wash of the Mediterranean, Scott did not notice that Zelda and the aviator Edouard Jozan were becoming closer, but everyone else on the Riviera did. Rumor began to quicken and race, as her oblivious husband remained lost in the pages of his novel.
But oblivion, like love, can’t be trusted to last forever. “The Big Crisis” came on July 13, Scott wrote in his ledger. Two weeks after the papers recalled the Hall-Mills case, matters appear to have come to a head over Zelda’s feelings for Jozan. Stories differ, as they always do. Some say that Zelda asked Fitzgerald for a divorce, telling him that she wanted to chase her chance for happiness; others that Scott confronted her and demanded that she end whatever was happening. Gossip has been speculating about what exactly that was ever since. Zelda’s romance with Jozan may have been a serious affair, or as insubstantial as a flirtation and a moonlight kiss. But it is clear that for Scott and Zelda, the affair, whatever its particulars, was deeply damaging; Zelda genuinely cared for Jozan, it seems, and Scott did not forgive easily.