In an interview with Ear Milk, Billie explains:

That song is the most special to me on the EP, because it’s straight from myself. The whole song is supposed to be singing to yourself in a reflection. It came about while we were writing “COPYCAT,” which is obviously about a person doing exactly what you do. “idontwannabeyouanymore” actually has the same chords as the bridge of “COPYCAT” because we wrote them as the same song. So the idea was to write a song completely opposite to “COPYCAT.” I go through a lot of depression, I have for most of my life, and I know so many people have the same issues as I do and most people don’t have a way of expressing that. They keep it inside them and are hurt by themselves, and I want to have music that people can listen to. If I write a song that you feel like you relate to, and when you hear it you go “that’s my song” – it’s yours! With “idontwannabeyouanymore,” I just want people to know they can feel that way and not be alone. That song is very deep in me. And the production is very R&B and it has that 1, 2, 3 rhythm, almost like a ballroom dance. But I didn’t want it to be overproduced. I wanted it to be simple and intimate. There’s a lot of tension and release in that song.

Billie said on her Instagram that ‘idontwannabeyouanymore’ was a deep song about her feelings:

idontwannabeyouanymore is a very inside of me song that has finally come out so if youd like to hear deep inside my HEAD and feel my FEELINGS GOO LISTEN