How do you keep a friend from hurting themselves?
Get them help you just can't sit there and watch your friend hurt them self. Maybe you should really have them sit down and talk with you and maybe you should ask them why do they want to hurt them self. Btw I know this feeling it sucks :(
Try to complement them, or tell them something about you that may be true or not
tel them thing to make them feel better about themself.........