Gatspy's friendship

As I read this book, Gatspy, who was some great mysterious character, turned more into a desperate man, who relied on money to fix the lack of love and friendship in his life. I don't think his relationship with Nick was very close. True, they may have spent a fair amount of time around each other, but Nick did not know anything about Gatspy, everything that Gatspy told nick, nick contemplated on whether or not it was true.
It seems to me that Gatspy, more or less, used Nick as a tool to establish a renewed relationship with Daisy. Gatspy, wasn't even a real person. Gatspy was a person that James Gatz envisioned, someone he thought that people, like Daisy, would want. It was interesting to me that Gatspy spent a great amount of time inviting people to his home and socializing, yet noone came to his funeral.
I think Nick spent time with Gatspy, because Nick wanted to believe in the things Gatspy told him. He found him intriguing, someone different and mysterious. I think that he wanted people to come to the funeral, because he wanted to believe that Gatspy, a man he was so interested in, was someone that everyone else loved. Maybe he wanted people to go to the funeral because he felt guilty, feeling like Gatspy's death was partly his fault. After all, it was Nick who arranged Daisy and Gatspy to meet up again.
I think he told Mr. Gatz that he was a good friend of Gatspy because he wanted Mr. Gatz to feel like his son had a friend. I also think he believed he was a friend, at least as close of a friend as Gatspy really had.