After Gatsby's death and funeral, Nick found himself confronted with the falseness of the life he had been living and the futility of the lives of the people he knew in the East. They all, including himself, had dreams and great plans for the future, but none of those goals had a realistic chance of being achieved. Nick at least has the honesty within himself to recognize this fact and to accept the emptiness of the lifestyle he had been pursuing. His conclusion, reached as the New England fall became late autumn, was that he needed to leave, to return to his Midwestern roots and values.
When the blue smoke of brittle leaves was in the air and the wind blew the wet laundry stiff on the line I decided to come back home.
Nick visits Jordan one last time and has a chance encounter with Tom Buchanan. Both meetings leave him feeling some regret about the way things turned out but also confident in his interpretation that they were empty people living empty lives, and that he was better off without them complicating his future.