For those who say that they want to learn this on piano, don't be disillusioned- it's hard. It sounds easy, but I'm an accomplished level nine jazz/classical/rock pianist and it still took me a while to get the phrasing and emotion right.
As for the meaning, I think it's just about doing what's better for you, even though it hurts. It might be like drug addicts; I bet it's a pain to stop, but it's better in the end, right? I like it. And it's the only pop song I like.