With BPD feelings equal facts. As you know, it's easy for a calm discussion to go off the rails. Since it's a shame-based disorder, they are very sensitive to perceived criticism and can feel attacked just because you have a difference in opinion.
I've had to learn new communication skills to express myself and learning how not to be invalidating has made a big difference.
https://bpdfamily.com/content/communication-skills-dont-be-invalidatingTo thrive in a relationship with a BPD partner, you have to develop a thick skin and not be affected by those horrible things they say when dysregulated. Easier said than done.
Remember too, do not take responsibility for their behavior. They are in charge of themselves. You didn't cause them to behave poorly. That was their choice.