Answer: he is an outsider in this community.
One of the reasons why Nick is a good narrator is the fact that he is always somewhat untouched by the problems that we encounter throughout the book. From the beginning, it is clear that Nick is an outsider. He has not been raised in the city with all the luxury that his new friends have enjoyed. Moreover, he does not have the money that other characters have. The fact that he was only planning to stay for a short time demonstrates how he is an outsider in the community.