Hi Imnotalone-
And

I'm sorry you're going through that, it is very painful and confusing, and unfortunately not unique around here, but you will go
through it. And you're right, you're not alone.
To answer your question, borderlines feel emotions intensely and think in black and white instead of shades of gray, so to deal with the end of a relationship, which a borderline interprets as the loss of an attachment, you may need to be all bad, when you were all good, and a borderline will use psychological tools like compartmentalization and projection to make you not exist at all or make everything your fault, in order to not feel the feelings of abandonment and likely shame. Standard borderline there, and we all do that kind of thing to some extent, with borderlines it's just more intense.
So how are you doing emotionally as you begin your detachment?