Nick and Jay

Both Nick and Jay are quite mysterious. From the book, it's mostly Nick or Jay's point of view. We learn more about the other characters than we do about Nick and Jay. It seems that Nick and Jay can trust each other. But, from the things that Jay tells Nick about his past, is it the truth? I can't help but suspect that both Nick and Jay are tying to cover up their "true" identity. Jay seems shady and sneaky. With him pretending to be what he's not (the fake books, enormous parties with random people) gives away the fact that he is not truthful and that he has a part of him that he wants to "forget."
The relationship between Nick and Jay is more so to benefit each other rather than a friendly relationship. In chapter 4 and 5, Jay tries to meet up with Daisy, and uses the help from Nick. To thank him, Jay wants to use money to "pay" Nick back. If they were really friends, doing something as simple as setting up an arrangement should not involve money to pay back the favor.