He has already threatened my guy and told him to stay away from me. My brother is also monitoring my activity on social media. He simply doesn’t trust me and is unnecessarily interfering in my personal space.
What has stopped you from asking him why he is doing so? Also, why haven’t you discussed it with your parents. May be there is a reason why he is doing it. You are reacting to the situation but not finding out why it is happening. Talk to him and your parents and settle it amicably.