It’s hard to know exactly what The Great Gatsby’s ending means.
The first interpretation is that it represents the fall of the American dream. In this reading, Gatsby dies because he has tried to live his life according to a dream—and not a realistic one, at that. This interpretation suggests that he deserved what happened to him: he got what he deserved.
The second interpretation is that it is a tragedy, with Gatsby’s death representing the ultimate loss. In this reading, Gatsby dies because he never gets over his love for Daisy; even when she doesn’t love him back anymore and even when she doesn’t care about him anymore, he still loves her and wants her for himself. This interpretation suggests that Gatsby was just too much of an idealist for his own good—that the world doesn’t really work the way we wish it would work sometimes; and if you try to force things into place that don’t belong there, then you’ll get hurt in some way or another.
It could also be seen as a commentary on the hollowness of the upper class. In this reading
