That one isn't one of my favorites.
If he is hurting himself you probably want to get him into therapy. Do you know much about cutting and self-mutilation? I started when I was 8. Often self-mutilation is about control. The child feels like (s)he has no way of controlling life but the kid can control how much pain they feel. It's a really difficult situation overall.
I think of cutting as a tool to help me manage my anxiety. It's not a great tool. It's kind of like pulling out an sledgehammer if you want to put a thumb tack in the wall. Sometimes it is all I have so I do it. (I haven't in over a year. I'm trying to not model it for my kids.) But it's a serious compulsive habit to get into. You will probably need a professional to help your son work through how to develop other coping skills. Sometimes there are things that laypeople/parents just can't teach. It's not because you are a bad mom. Cutting is really serious stuff. It's complicated. It's layered.
Good luck. I'm sorry the road is rough right now.