BPD is a spectrum disorder, and some people have it more intensely than others. we have lots of posters w/BPD come here who are aware of their condition and are mortified at how they treat others and want to stop doing it. some on the other hand have little awareness, and can only blame others for their own actions and choices. my wife certainly treated me as the person whose job it was to supplete her emotional needs, but little more than that.
so pondering how "they" think won't necessarily illuminate how your SO thought SlyQQ. we have a video,
What is BPD, which will help to explain the experience of having BPD.