Why is Nick on Gatsby's side at the end of the novel?

Nick gradually becomes disgusted with the carelessness and dishonesty of the other characters. As far as the Buchanans are concerned, Daisy and Tom both cheat on each other throughout the novel. Daisy cheats on Tom with Gatsby, and Tom cheats on Daisy with Myrtle Wilson. While it is true that Gatsby is enabling Daisy's infidelity by having an affair with her, Gatsby does not have a spouse and he hopes to marry Daisy sometime in the future. Also, Gatsby seems to be genuinely in love with Daisy, unlike Tom, who seems to consider Daisy more of a possession meant to be protected. Conversely, Gatsby proves himself to be a very unselfish individual. He hosts lavish parties for anyone who wishes to come, and when Myrtle dies, he readily accepts blame for the death despite the fact that it was Daisy who killed her. In all, Gatsby is a man of principle. Outside of his business practices, Gatsby is honest, caring, and reliable, and the difference between Gatsby and the Buchanans is perhaps most evident at the end of the novel when, in the wake of Gatsby's death, Daisy and Tom leave East Egg without leaving an address or contact information for Nick, who is left to deal with Gatsby's funeral, a funeral which Daisy and Tom do not attend.