Hi there
Thanks for your letter. It sounds as though this boy in your school is a bit of a nuisance and not very nice to know either. Your body is private to you and your space. He should not be doing this to you.
Your friend is right that you should go together and tell your teacher. You will probably want to tell your mum and dad, or whoever looks after you, about the boy as well. It's important that until you tell someone that you should try and not be alone with this boy.
This may feel a bit of a scary thing to do. But it is really important that you do tell someone because what he is doing is not acceptable. Remember you are not in any trouble because you haven't done anything wrong.
Have a look at the ChildLine message boards and send in a post and see what other young people think you should do as well.
Good luck and take care
Sam