Honestly I had a relative hard time trying to think of concepts for this illustration. I Toyed with ideas of using abstract form to represent love unreturned. I looked up classic examples of it in literature, song, and movies. There were two that stood out to me: Catch the Wind by Donovan and Return to Sender by Elvis Presley. I don't think it's very possible to draw wind, so I decided on on making a very simple illustration of Elvis's song.
I did some research on Elvis, trying to find an example of unrequited love in his life. Her name was Priscilla. They were married at first, but after she left him for her karate teacher (My thoughts mostly consist of, "lol, what?"). Apparently this had a huge impact on his ego and he was never quite the same after. I had my ammunition ready for this illustration.
From here it's a simple matter of placing the image into illustrator and making it look all crispy with good typography and a good stamp effect for "Return to Sender."