Is when a person is madly in love with someone, and the one she/he loves does not return the love. Often, the person in love tries desperately to show her love, but to no avail.
The person may feel rejection, depression, mania, or anxiety, because her love isn't returned, but it doesn't stop her from devoting all her love anyhow.
She may feel like she's going crazy!
Euphoria Godsent, wrote a song about unrequited love called, "Maybe You"ll Love Me."
The lyrics are, Why do you hate me? Always reject me. Seems like everything I do, it's never enough for you. Why do you neglect me? I feel like I'm nothing....