I do this too. I stopped cutting long ago, but I still do the forms of self harm that aren't so obvious. I figure it's the lesser evil. I think the way people usually stop it is the same as for other self-harm. Just try to talk to someone or use a coping skill when you get the urge. I think you should tell your school counselor, they deal with more then you would think on a day to day basis! I wouldn't be surprised at all if they have seen another person with trichotillomania before.