I take back my opening statement.
This song is not about change. This song is about the truth. People don't change, they are just covered with mess, like onions; full of layers. When you first meet a person, she is already real. When she's nice, and all sweetness surrounds her, that's part of her outer layers. But when you get to know her deeply, you see her inner layers; monsters. Ergo we can't really say they change. It's just what they're made of. And that my friend is the ugly truth.
Disclaimer: This post is not necessarily true.