Why is Nick "confused and a little disgusted" when he leaves the Buchanan's house?
Nick feels that Tom and Daisy are putting on a show and that the show is of dubious quality. He remarks on Daisy’s insincerity when she speaks of being “sophisticated” and he is also presented with the news that Tom “has a woman in New York.”
The Midwestern circle that Nick has come from was not nearly as volatile and obviously based on pretense as the one he suddenly finds himself in with the Buchannon’s.
It is no surprise that Nick would be disgusted and confused considering what he goes through at the dinner party. Instead of being invited to a friendly meal, he is witness to shocking martial strife, in-fighting and squabbling, to adultery and false pretense, and to a culture that seems to have no moral center.