Charlie and Sebastian are old friends. Sebastian is emotionally damaged. Charlie seems to have a life and is committed to his friendship with Sebastian.
Sebastian has stalled emotionally while Charlie has continued to grow up. Charlie meets a new love interest and this causes a fracture in his friendship with Sebastian. Sebastian is very very needy of Charlie's friendship and Charlie does not want to hurt Sebastian by following through on his new found love relationship by having to totally leave Sebastian.
The fact that each character is gay is not made into a factor with this story. It's just fact. The story is all about friendship, commitment, and the love of two friends - not two lovers. One friend is weak and confused, the other is strong and wants to get on with life but his conscience and friendship with poor Sebastian is a stumbling point with Charlie.
The characters are wealthy and spoiled. Sebastian's needy personality will get on your nerves but the plot works and you begin to care about Charlie as he is a nice person who is dealing with issues that have a direct impact on his life and future.