How does Fitzgerald prove in his novel, The Great Gatsby, that money can't buy happiness?

Gatsby fell in love with Daisy when he was young and poor. She married her husband due to money. Gatsby corrupted his morals in order to become rich and to be everything Daisy wanted. He hated the lifestyle he was living, but went through it for Daisy. However, when Daisy had to make a choice, she still chose her husband.