What do I do in the face of someone with bpd trying to hurt me for a reaction out of me? How to escape splitting? Or discard?
Hey 3000, welcome to the forums and I'm so sorry you're going through this. Many of us have had similar experiences and I know how gut-wrenching it can be. You asked a lot of questions and our members will get to all of them in time, but I wanted to touch on the more important ones now FOR YOUR MENTAL HEALTH.
You must understand that she's mentally ill and has a lot of conflicting emotions. People with BPD will overthink things and when it comes to relationships, they can self-sabotage through negative thoughts and emotions. In a nutshell, the relationship was that one extra thing that she simply wasn't prepared to handle, so she responded badly. It helps to understand that she's doing this because she's hurting so deeply herself as she tries to find answers.
First question- what to do when someone with BPD tries to hurt you?
Answer- recognize where it's coming from and don't let it hurt you. She's responding to deep-seeded trauma that she has no idea how to deal with, yet she expects you to support her and help her through it. If she can't verbalize it, then you surely can't help in any way, and that's where her frustration kicks in. Why can't you solve this thing I can't understand myself? You're a jerk for letting me down and ruining this for me. That's a very basic illustration of her mentality.
So what do you do? Pay less attention to the words and focus on the emotion behind those words. For instance, if you and I were hanging out and I appeared sad, what would you say? If I was angry...same thing. If I saw those emotions in you and you were my friend, my goal would be to help you process through those emotions with empathy and understanding. To do that, I'd have to listen. Tell me what's wrong, what happened. And as you talked it out with someone who cares and genuinely wants to help, you'd begin to relax and feel a little bit better.
That's what you do- stop defending yourself and stop arguing. You can be right or you can make this work- which matters more? You can't have both until she's stable emotionally, and that takes nurturing communication. Once she levels out you can have a productive conversation.
Questions two and three are the same answers. To escape splitting and discarding, you communicate differently, you show empathy and compassion, and you stop arguing about things that don't matter. Her mental health matters...as does yours. If you're arguing to prove her wrong, then she sees it as you being part of her problem instead of being part of the solution. She's struggling so hard with x, y, and z....and her boyfriend doesn't support her or understand her. He only cares about being right! (Again, this is her viewpoint, not mine. To fix this, her viewpoint matters though!)
I feel for you and none of this is fair, but you just got a crash course on mental health and what it's like to be in her situation. This is not your fault...but it's not entirely her fault either. She can't help that she has a mental illness that makes her over-analyze everything and get depressed, furious, or whatever her emotions bring. She hates that as much as you do, but she doesn't know how to control it.
It's your job simply to be a part of the solution. That doesn't mean "fix her" because you can't, not even a therapist can. She can fix herself though by changing her focus and viewpoints, and that takes a tremendous amount of support from those that are closest to her.
I hope that helped and again, I'm so sorry for what you're going through. It's not fair and it's not fun, but it is the path you're choosing and empathy is the only way forward. Check out the sticky tabs at the top of the page for practical techniques to lead with empathy.