The love Triangle between Daisy, Tom and Gatsby is the most prominent source of unrequited love in the novel. While Tom loves Daisy, Daisy only loves Gatsby. Gatsby expects Daisy to tell him that she has only ever loved him, because he has only ever loved her. But that's not true. During their five year hiatus, Gatsby's love was unreturned as Daisy loved Tom.
Finally, the love that George has for Myrtle is as unreturned as any other in the novel. George loves Myrtle with all of his heart, but Myrtle is too materialistic to love George's poor lifestyle. Therefore, she found a way out in Tom. Myrtle loves Tom, but this love is also unrequited. Tom only uses her as an outlet for what he can't get from Daisy.
Source: The Great Gatsby.