I'm pretty sure (I figured this out from watching the music video: D) that it means that she's loved before, but she never knew it could get so much deeper ("I never loved nobody fully") and could feel so good. "I hear in my mind, all of these voices, I hear in my mind, all these words, I hear in my mind, all of this music." In the video her lover was first just a mannequin and then it was a real person, and it went from just black-and-white to colour. I love this song, it's so refreshing :)