It's all about sexual fantasy and its power over your life and state of mind. The thing is, all the little vignettes end frustratingly, with no conclusion or explanation. These are glimpses into subterranean stories/fantasies; the junky girl at the party, kidman's revelation of her desire and willingness to fvck that dude, the whore in the costume shop, and finally the big orgy. All of these vignettes have some form of pretense and dishonesty involved that fvcks it all up and makes it end frustratingly. In the end he comes clean and is honest, and kidman replies, "we need a good fvck" (or something like that). If you are just honest, all these problems don't appear.
I also loved the cinematography and use of color. Very saturated reds and blues are used throughout the movie. I think of the reds as denoting the passion and build up of the sexual tension, and the blues as the frustration and anticlimax that comes with any of the problems that arise.
Well, that's my interpretation. The beautiful thing about kubric movies is that they give you so much room for interpretation. I think that EWS is kubric's most underrated movie, and hasn't gotten the recognition it deserves.