At the end of the novel, Gatsby is killed. He is shot by George Wilson who wrongly believes that Gatsby was the one having an affair with his wife and was responsible for her death.
The pool in Gatsby's house is also a significant symbol. When he is killed in the pool, it's like his false world, built on parties and a facade of wealth, comes crashing down. The pool which was once a place of luxury and excess becomes the site of his tragic end, symbolizing the futility of his attempts to create a new identity just to win Daisy.
At the end of the novel, Gatsby is shot and killed. His death is a result of a misunderstanding and the chaos that ensues from the affairs and secrets of the other characters. It's a sad and unexpected end for him.
Another theme is the inevitability of the past. Gatsby is so fixated on his past relationship with Daisy that he can't move forward. In the end, his inability to let go of the past dooms him. The past has a powerful hold on the characters, and they struggle to break free from it throughout the novel.
The green light is a major symbol. By the end, it's clear that it was not just a physical light across the bay, but a symbol of Gatsby's unfulfilled desires. His whole life was centered around that light, which was Daisy in essence. But as things fall apart, the light fades in significance, highlighting how his dream was ultimately unachievable.
Nick's final words are a condemnation of the upper - class society he has witnessed. He realizes that the American Dream as represented by Gatsby's pursuit was a false one. Nick says that Gatsby believed in the green light, in the orgastic future that year by year recedes before us. It was this dream that led Gatsby to his downfall, and Nick sees the tragedy in that. The wealthy, like Tom and Daisy, were just using people and then discarding them when they were no longer useful, and Nick was left to pick up the pieces and tell the story.
One possible significance is that it represents his final attempt to escape his past and the illusions he had in the East. Moving west could symbolize a fresh start, away from the corruption and false hopes associated with the East in the story.
In 'The Great Gatsby', the final irony is that Gatsby, who has spent years amassing wealth and throwing lavish parties all in an attempt to win Daisy back, dies alone. His parties were full of people who didn't really know him or care about him. And in the end, Daisy doesn't even attend his funeral. All his efforts to be part of the upper - class world and win Daisy's love amount to nothing. It's ironic that his grand dreams and all his material possessions couldn't buy him the one thing he truly desired - love and acceptance.