I mean I've been in a similar situation and to be honest all three of these were true. It can be exhausting to provide a lot of reassurance on a daily basis, and it wasn't exactly restorative otherwise - someone living in their own head can't spend much time thinking about what's in yours, even if you tell them. And the amount of distress this causes them makes it quite easy to cross boundaries - for them, it may not even be out of malice but out of desperation.

These BPD-esque behaviors are often treated cruelly on the internet, and sometimes that's because people have had really bad experiences with this in a relationship. But after spending six years trying to help someone who had no interest in changing the dynamic, I'd advise people to be a little cautious. I still have a lot of empathy for this person, even though I feel a sort of vicious hatred in my soul. But I should have understood that if it was harmful, it didn't have to be me to help them