When Nick leaves the Buchanans' house, he is “confused and a little disgusted.” Why?

In The Great Gatsby, this entire
scene has an unreal atmosphere about it for Nick.  When he enters the house through a
high hallway the windows gleam white and the grass outside seems to grow into the house,
and the wind blows curtains and blows the women's dresses, and the women appear to float
above the couch.  This has the feeling of illusion, which, of course, Nick discovers the
relationship between Tom and Daisy is. 

From Nick's
entrance into the house, until the time he leaves, Nick is a bit dazed and confused. 
Notice that he is always a little behind the others, without knowledge that they
possess. 

Jordan acts like he isn't even there, and of
course he doesn't even know who she is.  The others talk about Jordan's career while
Nick stands by unknowing.  Tom has a new book full of stale ideas to share.  Tom gets a
phone call and the women know who the caller is and what the call is about, while Nick
doesn't.  

The atmosphere and the personalities and details
involved, combine to create a bit of a surreal experience for
Nick. 

It's no wonder he leaves feeling "confused and a
little disgusted."