Gatsby wants to be with Daisy. He wants to be with her because she is the only person who can make him feel whole. He wants to show her that he’s come from nothing and has built himself up into something, and he wants to do that by showing off his wealth and power—something he feels he’ll never have if he’s not with her.
He also wants Daisy to see him as a man, not just a boy, so that she can really see why he loves her so much.