I seriously understand how you can do it, been there. And making you expose self-harm or objects only makes it worse. Obviously you've got a lot of pain and/or frustration and this is a way of letting it out. I went through a wicked cutting phase during highs-school and my friends knew I was doing it. I carried on doing it until a friend told me that I had better tell him what's so bad that I physically have to hurt myself to get relief??So I told him what was going on and solved it. I realised that the issues I had been harbouring were unrealistic and that I wasn't the waste of flesh I thought I was.
Point is, whatever you think you cant say, whatever you feel you aren't aloud to feel, find someone you look up to and ask if you cant take a few minutes of their time say it and just hear what they have to say. Even if you just blurt out the words, at least its been said.
You'll feel the weight lifted.