Granite is right. Relapse can happen, but it doesn't mean you are a failure. 3 years is a long time to go without self-harm and you should be celebrating that! About 3 months ago, I decided to try and stop self harming, didn't pan out and went back to into it once a month. (give or take) BUT! For the last month I finally stopped.
Knowing people can stop for 3 years is amazing. I applaud you. I have a lot of faith that you can stop again and continue on your road to recovery.