The men in Gatsby's world:
Nick is the narrator of the novel and becomes Gatsby's only true friend. This can be inferred by the fact that Gatsby confides in Nick and that Nick is one of the few who attend Gatsby's funeral, although so many attend his parties.
Tom is Gatsby's rival for Daisy. He is Daisy's husband and although Daisy has an affair with Gatsby, she can't do as he asks and erase the past by saying she never loved Tom.
Meyer is a business associate of Gatsby's. He is a gambler and known criminal. Gatsby's association with him lets the reader know that his business might not be completely above board.
The women in Gatsby's world:
Daisy is the love of Gatsby's life. He has a brief affair with her five years before the story starts but never loses his desire for her and everything she represents to him.
Jordan, in a sense, is an ally for Gatsby. She is close to Daisy and believes that Daisy deserves a little happiness in her life, so she helps Nick arrange a reunion between Gatsby and Daisy.
I guess you could say that Pammy, Daisy's daughter, is in Gatsby's life. He doesn't really think about her, but when he meets her, it is a turning point in his life. He can't deny then that Daisy and Tom have a past and things start to unravel after this point.