Why did Nick feel awkward at Gatspy's party?

I presume that this is regarding the second party, when Tom and Daisy attended. In the first party he was no more awkward than normal and appeared to enjoy himself.

In the second party, however, it is important to remember that Daisy is now having an affair with Gatsby, and has invited her husband to a party given by Gatsby, as such, this is a difficult situation and because Nick knows this, and feel self conscious, the evening is understandably awkward.