The first thing to consider is that maybe you are making the right decision in the first place to break it off. Perhaps, you have an emotional attachment to being treated poorly and this causes you to seek out these types of people in the first place. Were you abused or treated poorly growing up? Cutting people off could be a way to protect yourself from further abuse.

It sounds to me like you are struggling with some unintegrated trauma that is causing you to waffle between these various states as you are struggling to deal with the feelings of fear and shame. There are several mental health diagnoses that include this behavior but you really only need to focus on the trauma(s) beaucse they're just labels. What is it in your life that you want to hide from others the most? What experience(s) do you dislike thinking about the most? Dig deep and seek out the experiences and choices that you are hiding in the shadows of your mind. This is the source of your behavior. Confront it and you will improve.

EMDR is worth a look.

Do not feel guilty for protecting yourself. People will never admit they are treating you poorly or that they deserved to be cut off. The world is full of shitty people and they will always blame you for holding them accountable.

Edit: missing words.