Conrad Sewell wrote this stripped-back ballad when he was in the middle of a relationship and had started to realize his actions were affecting his girlfriend. She was always upset and he would often arrive home to find her crying. He had to acknowledge she wasn't the same person as when they first started dating, and this was because of the way he was behaving.
"Changing" is a song of apology for everything Sewell had done. The singer explained in a press release he's "telling her to never change for anyone because you're perfect the way you are. Especially don't change for me because I wasn't worth it at the time."