I'm Like A Bird by Nelly Furtado
I think it means she don't love you, but she knows you love her. She is who she is, and will love who ever she feels like. Just because you are in love with her doesn't mean you actually know her. The fact you've loved her and this love was never reciprocated makes her sad, she never wanted to hurt you. Dont ever try and change her because she will always just fly away