How is Nick's attitude toward Gatsby ambivalent even at the moment wen he says goodbye to him?

At this point in the novel, Nick feels very strongly that
Gatsbty is the best of the bunch he has asociated with.  But he does not realize just
how callous and self centered Tom, Daisy, Jordan, and even Meyer Wolfshiem are until
after Gatsby's death.  When the only two people who come to Gatdby's funeral are his
father and "owl eyes", Nick realizes that Gatsby's love of Daisy was real, that he was
real, even though his background wasn't. At this point his ambivalence for Gatsby is
gone, and his feelings towards everyone else he has met in the east are sealed.  This is
why he goes back to the mid-west at the end of the novel.