I think you need to not use the language "addiction" and "relapse". It is a maladaptive coping mechanism. You can't cope with your emotions and stress, so this is what you do.

The very fact that you consider you "relapsed" like a drug addict, has caused you so much guilt that you are further self harming. Can't you see how viewing it in this manner is not constructive but is aggravating your problem?

If you have BPD, there are some specific types of therapy which may be of assistance. You need to train yourself to use other methods to deal with your emotions, and learn methods to dissipate building emotions before they result in a crisis.

I used to self harm- severely. My whole body is covered in MASSIVE, GROSS scars, several hundred of them, everywhere except my head. I won't go into more graphic detail, but I have numerous operations and surgery due to damage. So I know a little about this issue.

I have not self harmed in over a decade.

You also seem to suffer a lot of guilty, your own guilt towards self harming is triggering further self harm.

Please see a professional therapist.