What are some songs that are about being in love with someone who doesn't love you but you don't know it?

So basically, what are some songs about thinking you're in love with someone who doesn't love you and in reality the person you truly love is with you and the person you think you love truly loves their person. I'm specifically looking for a song that represent the complicated love situation of Scarlett O'Hara in Gone With the Wind. She thinks she loves Ashley, but she really loves Rhett and Ashley really loves Melanie.