Wsit what did he do to that black haired dude again. I haven't read this in a while

if u mean what did mc do to the ml, when they were kids mc was popular and ml was a small, quiet kid but became seatmates and got along and i think mc stopped his friends from picking on him (i think, its been more than a year since i read) but one day mc and his friends go back to the classroom and see ml is sniffing mcs gym clothes crazy style which grosses him out and from that point he lets his friends bully him and even joins in. one day ml gets too close to him and mcs is disgusted by him so he shoves ml away but theyre near the top of a staircase and he falls and hurts his head pretty bad. since that day ml wants revenge and mc feels guilt