How do we know, even before he dies, that Gatsby will never have Daisy?

Jay and Daisy have very little in common when it comes right down to it. They are simply infatuated with one another; Daisy has been corrupted by the lifestyle that her husband has provided for her. Even though Jay's wealth has been obtained illegally, he is much more naive and innocent than Daisy. It is nearly predetermined that she will end up with Tom by the end of the novel.