[popsicle]

Maybe you should tell your friends and family the truth. I can see where you're coming from, but they will be able to help you better if you're honest.
Why did your best friend call you pathetic? If it was over the cutting, realize that she probably doesn't understand what it's like for you (though that doesn't make it okay for her to say that) and she could just be worried about you. I was in a similar situation about a year ago- I had a best friend who called me a mess and threatened to tell the guidance counselor or my mother and all that. She also made me cry a few times. Very stressful. I was angry at her for a long time, but realizing she was acting on worry from the situation helped me forgive her.
Is your best friend the only thing that triggers you, and has she been triggering you for a long time? How does she do it other than the things you mentioned in your post?
Sorry if I'm seeming invasive, I'm just trying to get a good idea of your situation so I can give you some advice that's less general and pertains more to you.
I think it's important that you see a therapist if possible. It might be helpful if you talked to the guidance counselor yourself, but if your parents are supportive maybe they can get you help. It seems like talking to somebody would be good for you.
Also, throwing out any of the tools you normally use can be helpful. That way you're not tempted by something in immediate reach.