Hi Anxiathy, welcome to the group

it's totally fine here to share at a level that works for you, so please know you can take your time and "be in the driver's seat" about what you disclose.
Even a "normal" breakup is painful at a core level, and breakups with pwBPD aren't "normal".
You two were together for four years -- I'm curious what happened along the way to lead you to suspecting BPD?
Did your ex initiate the breakup, or did you, or... other?
Tell me a little more about this (if you're okay with it):
We were supposed to break no contact again today and I'm struggling to not make that happen myself.
Am I tracking with you that the two of you had an agreement to reach out to each other on a certain day?
I just miss her horribly and want desperately want someone back they may have never even been there in the first place.
That's a whole other layer of pain to BPD relationships and breakups -- that pwBPD (whether diagnosed or not) struggle to have a real self. Was the "good" one the "real her?" Who was it you were with, anyway?
The pain and loneliness are so heavy. How are you doing with all of that today? Fill us in whenever works for you, and, again, at any level of detail that you personally are okay with.
-kells76