Jordan's history of the relationship between Gatsby and Daisy, as told to Nick, reveals that, in the summer of 1917, Daisy met and became quite infatuated with an officer from the nearby Camp Taylor, a Lieutenant Gatsby. Her family prevented her from continuing to keep in contact with him.
After giving the impression of being engaged to someone from New Orleans in February of 1919, Daisy actually married Tom Buchanan of Chicago in June, 1919. Jordan was one of the bridesmaids. Shortly before the rehearsal dinner, Jordan found Daisy "as drunk as a monkey." Daisy slurred her way through announcing that she had "change' her mine!" and didn't want the expensive pearl necklace Tom had given her as a wedding present. Through the tears and attempts to sober Daisy up, she never let go of a letter that seemed to be the cause of her distress. While it's never directly stated in the story, the impression is that the letter was a declaration of his continuing love for her from Gatsby.