He talked a lot about the past, and I gathered that he wanted to recover something, some idea of himself perhaps, that had gone into loving Daisy. His life had been confused and disordered since then, but if he could return to a certain starting place and go over it all slowly, he could find out what that thing was.

F. Scott Fitzgerald

The Great Gatsby. Chapter 6, Gatsby has not moved on from his past but is obsessed with trying to recreate. That was the time he had Daisy in his life and was happiest.