I personally believe that this song may be about her best friend stealing the man she loved from her. Things weren't going well between them, they got in fights and hurt each other as suggested by the first two verses. And in the chorus she says "and I'll leave him just for you" so considering how much she clearly loved him (as is portrayed through the song) and yet she still left him, saying she'll 'shiver like she used to' (which I believe means shivering from the loneliness and lack of warmth she had from her significant other. Like being cold at night with no one to hold you) leads me to believe she hasn't left him for someone else she loves. So to me the only logical conclusion would be that in order to keep her friendship she left him, gave him up, for her friend.
I personally believe that this song may be about her best friend stealing the man she loved from her. Things weren't going well between them, they got in fights and hurt each other as suggested by the first two verses. And in the chorus she says "and I'll leave him just for you" so considering how much she clearly loved him (as is portrayed through the song) and yet she still left him, saying she'll 'shiver like she used to' (which I believe means shivering from the loneliness and lack of warmth she had from her significant other. Like being cold at night with no one to hold you) leads me to believe she hasn't left him for someone else she loves. So to me the only logical conclusion would be that in order to keep her friendship she left him, gave him up, for her friend.