Caught my roommate going through my personal things?

Well firstly if he is going through your stuff during the beginning of the school year and you barely know him, what is to stop him from going through your things later on in the year when he knows you better? I believe you have to confront him about the situation and ask if he needs something like toothpaste or paper maybe that he didn't have at the time. After you need to set standards about borrowing or using OPP(other peoples property). For example if he borrows your highlighter or sharpie, tell him to leave a note about using it. If your friendly and are cool with him borrowing your shirt or using your laptop then you need to set guidelines on the use of those things. Also if he denies that he was going through your things then here are some explanations as to why he could be going through it. 1. He is a spy from another country and its in his training to get to know things about the people around him. 2. He is some sort or weird pervert or a kleptomaniac. 3. He is an only child and its his first time sharing room space with others. Anyways definitely grasp the situation and resolve it before he does something worse without asking for permission.