Hi Work it out,
I'd like to join the other members in welcoming you to the forum. I'm sorry to hear that your relationship has broken down, at least from what it was; that is so painful. I understand what you mean by the relationship not being healthy—I felt that way, too. Unfortunately, it doesn't necessarily make it easier to detach.
You've come to the right place for support. Things really DO get better; they have for me, and they can for you, too. As

gotbushels said, I encourage you to read the steps on the right sidebar------> They will take you through the process of detachment.
I'd say the very first step, though, is a decision from you about what you want from this relationship. Do you want to attempt to be friends? Do you want to detach completely? There are various tools to use in each scenario; for example, building a friendship with someone with BPD/traits takes good communication skills, lots of validation, and very strong boundaries. Detachment requires a grieving of the loss, self-care, and work on our own dysfunctional patterns of relating (of course, all the tools are good for all relationships, too!).
Here is an article that really helped me to understand what I was dealing with after my breakup. Perhaps you've seen it? I'd love to hear your thoughts:
Surviving a Break-up when Your Partner has Borderline PersonalityKeep writing, Work it out. It helps a lot. We're here to support you.
heartandwhole