Nick says,"There are only pursued, the pursing, the busy and the tired".What does Nick mean? how doe each character in the novel fit into this schema?

I can't go through each character but consider "pursuit" as a theme in the story. Certainly Gatsby's whole life is the pursuit of something. Gatsby wanted wealth, acceptance into the world of the rich and (most importantly) Daisy. Gatsby is never happy always pursuing illusions that can't make him happy. This is about the same for most of the characters in the novel.