One of the things that makes BPD the hardest to live with, both for the person lover and for the loved, is the fact that it seems unpredictable when a stereotypical BPD response is going to emerge (for the Borderline person and for their partner). The standard response of the partner is to feel like they must ‘walk on egg shells’ to prevent the Borderline person from ‘flipping out’; but often the Borderline person often experiences this behavior as *distancing*, which exacerbates the sense of abandonment, which can then trigger the stereotypical BPD response. This is a complex, and interconnected set of forces, which are not really under anyone’s control. It’s the construal of the situation by the Borderline person that generates the response, but they have no control over how they construe the situation. Even worse, the stereotypical BPD response is likely to cultivate the situations that lead to actual abandonment. Yielding a situation where they feel justified in their worries about abandonment. This is part of the reason why it’s such an awful mental illness, both for the partner and for the Borderline person. Ok, now here’s the rub. Most of the time, in most interactions, the Borderline person will have control over their actions. They will be able to see that their partner loves them, recognize that their partner is committed to them, etc. They will be able to seek help and consider ways of making things better. But epistemically, the forces that lead to an episode will often feel unpredictable and as if they are coming from nowhere. Even worse, from the inside, they may well feel justified at the time, even if on reflection it is clear where they went wrong. As a consequence, within an episode, the Borderline person may not be aware that they are exhibiting problematic behavior.
BH on https://aphilosopherstake.com/2014/01/22/romantic-dysfunction-bpd-and-moral-responsibility/