Nick's departure from Jay Gatsby in Fitzgerald's The Great Gatsby is that of an epiphany. For Nick, the unreliable narrator of the novel, who waivers in his opinions of the main characters, finally realizes that Gatsby is the only truly genuine one of all:
"They're a rotten crowd....You're worth the whole damn bunch put together."
That Nick is an unreliable narrator is evident in many parts of the narrative. For instance, while Nick has been critical of Jordan Baker's amorality and her having cheated in a tournament, he, nonetheless, dates her and considers a serious relationship until he senses his loss of innocence and youth on his thirtieth birthday. In his association with the Buchanans, Nick has disdain for Tom's racist views, his careless immorality, and his cruelty to Myrtle Wilson; yet, he is somewhat impressed with him, saying wistfully,
"...while we were never intimate, I always had the impression that he approved of me."
Early in Fitzgerald's novel, Nick Carraway seeks to establish himself as a calm observer who is "inclined to reserve all judgments"; yet, ironically he becomes very involved in the lives of those he says he merely observes. In this involvement, Nick comes to the realization that the only truly genuine character is Gatsby, who remains true to his idealized love of Daisy. For this reason, Nick calls out to him, praising him. But, afterwards, his comment is ironic:
"I have always been glad that I said that. It was the only compliment I ever gave him because I disapproved of him from beginning to end."
Having disapproved of Gatsby "from beginning to end" certainly contradicts Nick's declaration of reserve of judgment from the early chapter, but it does indicate his epiphany about Gatsby's genuine--albeit tragic--nature. And, it establishes the unrelaible Nick as actually the moral center of the novel.
If you are asking whether Nick leaves Gatsby by car or on foot or whatever, it seems that he leaves on foot. He has been hanging around with Gatsby and then he goes towards the hedge between their two houses. So he is walking back to his house. He later goes to the train station and into New York City to work.
If you are asking about something else, I think there are a couple of important things:
- Gatsby is waiting for Daisy to call him when Nick leaves. He still thinks the two of them might have a future together. So when Nick leaves, Gatsby is sort of hopeful, but the hope seems to be fading.
- As Nick leaves, he turns around and shouts to Gatsby. The book says
“They’re a rotten crowd,” I shouted across the lawn. “You’re worth the whole damn bunch put together.”
So Nick leaves Gatsby with a compliment -- the only compliment he ever gave Gatsby.