Nick says, “There are only the pursued, the pursuing, the busy and the tired.” What does Nick mean? How does each character in the novel fit...

I think Nick means that there are really only two types of people in the world: those that are pursued and busy, and those that are pursuing and tired. Some people are pursued, or desired, and they must be pursued because they seem so busy; perhaps they are desirable because they seem so busy. This would include people like Daisy: she seems to have what looks like a full life from the outside. She's married, a mother, runs a large house, and keeps a full social schedule. She is desired by many: her husband (in a sense), Gatsby, her friends. I would also place Jordan in this category; she enjoys being pursued and desired, and she is too cool to seem to want anything or anyone too much.

Then there are the people who are pursuing someone or something, who desire something, and they do little besides make the effort to try to attain that thing. This would include Gatsby, who wants Daisy and has worked for years, attempting to earn enough money to tempt her and gain enough notoriety to be noticed by her. This also includes Myrtle and George Wilson. Myrtle pursues Tom, his money, and the lifestyle that he has and she wants; George pursues success and his wife's waning and wandering affections. This also includes Tom, who seems to always be chasing something, perhaps affection or the sense of being needed by someone, since his own wife seems not to feel much for him.

I'm not sure if Nick fits into either of these categories, or perhaps he has a foot in each. He is pursuing personal success, but he isn't single-minded about it the way the other pursuers are. He is also pursued, to an extent, by Gatsby and Daisy, and Jordan allows him to pursue her (which almost makes him the pursued one). He's a bit more three-dimensional than the others; or, at least, he is more dynamic, and these changes make him tougher to pin down.