This reply is a bit late, but I just want to say that you are yourself. You are the way you are. It helped me a lot to realize that. Nobody can fix me. I was born this way. You said, "[T]his demon follows me wherever I go." It's not a demon, it's the way we all are. And most importantly, that's not a bad thing. The sun can burn, but it also gives energy for plants to photosynthesize, which in turn feeds many animals including us.
You might say that taking medication changes you, but fundamentally we are all collections of atoms and molecules. We constantly change, so by that definition we are never the same. So in the abstract, this thing we call "us" never changes. It's just a title we give to the ever changing mass of complex processes we call humans.
Many people call the depression "darkness", but in reality it's the truth. It happens to us like any other thing. There is no universal law that states we must avoid the darkness. It is there, it is a part of us. I simply exist as spacedust attracted to the gravity well of planet Earth. The universe is shrouded in darkness, but we are in the light of a star.