Everytime she comes back and breaks NC...
Hi Algae,
I'm sorry about the cheating and walking away, this is difficult. I don't sense that you are getting healthy space for you to heal your wounds and gather strength to be able to deal with her behaviors. This takes time.
You can't control what your ex does but you can control you. What I mean is I don't put boundaries on my ex. I put them on myself. So if she does X Mutt reacts with Y.
What boundaries would you put on the self? What can you do if she is being needy, emotionally dysregulated, emotional immaturity, wonders off with another man and comes back?
Why are you worried about how you are going to be split? She's mentally ill, splitting is not something that she or we have control over.
Above all, take care of you.