Hi lwood,
Welcome and hello
It's not uncommon here for people to wonder if their partner is BPD. Even if your ex is sub-clinical or something else, the communication skills and lessons are very helpful.
We also have a helpful section on the Coparenting board about
Raising Resilient Kids When a Parent Has a BPD that can make a big difference to how you can help your kids make sense of what's happening.
Do you think it can help depersonalize the verbal attacks if you swap out the pronouns? Often, the degrading insults are projections, a very crude defense mechanism to help externalize negative feelings that people with BPD struggle to process. It's much easier to experience those emotions and thoughts when they are projected onto an intimate partner. "You are a terrible parent!" is often a projection of "I am a terrible parent."
If the verbal attacks escalate to the point where you are feeling intimidated, it can also be helpful to keep saying the same simple word over and over in a calm voice, like "Stop" or "No," holding up your hand if it helps.
There are other skills and lessons that can help manage the environment in the belief that this will minimize some of the conflict you experience. I hope you'll keep posting and let us know how you're doing. It takes a lot of strength to not be emotionally injured in a BPD relationship, and having some kind of peer support and/or a therapist is critical to your well-being.
We're here for you.
LnL