How can I stop saying the n word?

Firstly, I am neither black nor white, but I’ve got a white friend who always calls me the n word because my skin is brown, it’s not even dark, and I started saying it back. Now it sort of just slips out to whoever I’m talking too. Sometimes I’ll see someone and be like “sup n....”. On the first of november, I decided to also do no-n-word-november and i failed the first day because another friend was being annoying and the n-word just slipped out. How can i stop it? It’s become a habit and I want to get rid of it before It’s too late. I’m being dead serious, please help. Btw, I wouldn’t consider myself racist. Please give me some advice.