In Fitzgerald's The Great Gatsby, how is Jay different from his guests?

The most profound difference between Gatsby and his guests is that, unlike them, he is not a party reveler. He is reclusive and does not join in the ostentatious celebrations which he, ironically, has arranged and is paying for. Whilst the partygoers are there to enjoy themselves and revel in all sorts of flamboyant behavior, he remains aloof. This makes him a man of mystery around whom all sorts of gossip abound. Guests admit that they have never personally met him but each one has a juicy bit about him to share.

Many of his guests surmise that he is born of royalty, that he once killed a man, that he is involved in some or other nefarious scheme, and so on, but they are not quite sure about who or what he actually is. The reader does discover, though, that Jay Gatsby has been arranging these extravagant parties for a single-minded purpose. He wishes that his lost love, Daisy Buchanan, would attend one of them so that they may meet and reignite their relationship which had been abruptly interrupted when he had to leave for the war five years ago.

When Nick Carraway is invited to one of the parties, he is amazed at the variety of guests he encounters there. Most of them have gate-crashed and have been making a habit of coming to these over-the-top gatherings with the idea of just hanging out and enjoying the free food, alcohol and entertainment. They are literally leeching off Jay's benevolence and their behavior verges on the obscene. Nick mocks them by listing and commenting on their ludicrous names and titles.

When he finally meets Jay, Nick is surprised by his sober and gentlemanly behavior. He is immediately attracted to him, in contrast to the sentiments he expresses about Jay's guests whom he seems to regard with more than a hint of derision. Nick's genuine admiration is clear in the following extract from Chapter 3:

He smiled understandingly — much more than understandingly. It was one of those rare smiles with a quality of eternal reassurance in it, that you may come across four or five times in life...

...I was looking at an elegant young rough-neck, a year or two over thirty, whose elaborate formality of speech just missed being absurd. Some time before he introduced himself I’d got a strong impression that he was picking his words with care.

The two men become friends and Nick becomes Jay's confidante, although one cannot escape the suspicion that this only happens because Nick can bring Jay what he has so much wanted--Daisy. Even so, Nick, we discover, is the only real friend Jay has in the end. None of the party revelers or any of his known associates, not even Daisy, had ever been really close to him since none of them, except the man with owl eyes, four of five servants, the postman from West Egg and Gatsby's father, turn up at his funeral. Ultimately, once the party is really over, they disappear into the quickly dissipating mist of their revelry, never to be seen again.