This is a bery hard thig to do and you should be so proud for coming this far! I am a self-harmer and recently relapsed and I finally told my best friend. It was so hard for him to get his head around at first. I would say talking to them face to face is best but I have done it many ways for different friends.. My closest friend was obviously very worried and basically i "accidentally" rolled my sleeves up and he saw and we chatted for a while.
Trust me, once you get this out you'll feel much better. You could even write a letter, sing a song.. It may sound silly but some people can express better through songs :3
Well done and I hope your friend understands best to their ability.. Some people find it hard to believe that someone close to them has harmed themselves in such away. I think you can do this, you've already came far.. Message me if you want some more help or to chat etc
