Why did Nick say this about Gatsby in The Great Gatsby?

Nick is saying that Gatsby had been a good and special person even though he did try to take away the wife of another man. "What foul dust floated in the wake of his dreams" refers to the people that destroyed his dreams: the other morally lacking and superficial characters in the story such as Tom. "Abortive sorrows" and "short-winded elations" refer to the brief sadness and happiness of men. So basically, Nick is no longer interested in the worldly matters of men because of how Gatsby, a dreamer, was ruined by them.