I'm going to tell my brother to mind his own business.
Why would you tell your brother to mind his own business?
He thinks it's his duty to supervise my every action.
I understand it can be frustrating dealing with someone who you think is invading your privacy, but your brother is probably just trying to help. Being honest with family members is good because they can often help and give advice.
I still will demand him to stop. I'm tired of feeling guilty.
You don't have to feel guilty. I think if you tell him how it makes you feel, he will back off on his own.