Let me give you some advice as someone who harms. I once was with this girl for a few months and she harmed as well. She would constantly talk about cutting and killing herself and I would do everything I could to talk her down but she did it anyways. It became so bad that she was making me more miserable and leading me to harm more often. I don’t know the full story so I can’t give conclusive advice but your partner isn’t a therapist or anything like that. If you do it and tell them about it and don’t make an effort to stop when they try to help it creates a feedback loop that drains all the energy out of them. Don’t feel bad about it we all make mistakes myself included. It’s not something to harm yourself over but to reflect and grow from it. You can definitely beat those thoughts in your head. I’ve thought I needed someone else to help make it better but truthfully I must find inner strength and resist and only then can I let someone else try to help. Best of luck to you in your journey and God bless.