I can understand how you feel - I think a lot of us have been there. But puzzclar is right. Self-injury very quickly becomes addictive. What is just a 'one time' release turns into something that you need to do regularly to cope with the emotions. The addiction can be easily as strong as any others (drugs, alcohol etc). You begin craving it even stronger and it is hard to break.

Please try other things that can help you get those emotions out. Puzzclar gave some great examples And seeking professional help is always great too. They can help you come up with other strategies that don't involve harming yourself.