I'm thinking about cutting off my best friend for good.
Is there a reason why you want to cut off your best friend?
My friend was overly involved in my life and now they ruined it.
Friends shouldn't be ruining you so it's justifiable if you want to cut them out. Otherwise, they will drag you down and you won't be able to do the things you want to.
I'll always have control over my own life, regardless of who I'm friends with.
It's great that you feel you have agency in your life, but sometimes the people you associate with can bring you down. It's good to cut negative influences out of your life so that they don't drag you down.