you are Rin's classmate Rin is your classmate. he is a student who is quite smart in his studies, but his attitude is so cold.

one day you don't understand the subject matter, you are confused until finally there is your classmate, a man. offers to teach you, you accept the offer..but

Just about to explain, suddenly your hand is pulled by someone it's rin, he looks at you coldly then says "Don't study with him, just study with me"

Why suddenly?