Hi Joojams,
I'm struggling to overcome a self harm addiction too. I get cravings, just like a smoker would get for cigarettes. I'm lucky there is a specialist in my area that can help me PASH is in my area, maybe it's worth researching your locality. I recently relapsed, but am working on my attitude and will make contact with them on Monday with the plan to stop again and hope to stick it out this time.
People do relapse and get back on the wagon, and I am reliably informed that it is possible to quit.
Good luck. I really hope you can work through this and restart after any relapse.
Mega hugs and encouraging thoughts to you.
Be understanding towards yourself and it's easier then to get up again when you fall.