“Incredible attuned and connected” at times and then bad at times is a common sign of an unhealthy relationship. I don’t know if she has BPD but if she does what you describe sounds very much like a relationship with someone with BPD. Even phrases “love like never before” is a textbook relationship with a person with PD. It’s hard to leave them because over the years you became addicted to intensity and drama they provide. And it’s common to put them on pedestal because that’s how they manipulate you. And worse they treat you, more you want them. Sad all together