Hello gothope, I'd like to add my voice in welcoming you to the group.
It's difficult coming to the realization that lack of insight can be a feature of BPD -- not an accidental coincidence. Like Sancho mentioned:
It helps me knowing that this serious condition can take someone in and out of reality - and they have a strong belief that whatever they think is the truth.
While for more "biological" or "structural" issues such as schizophrenia or TBI, the lack of insight may have a physical cause (I think I have heard that brain lesions or damage can impact ability to have self-insight), to the best of my knowledge there is no obvious physical cause for lack of insight with BPD. However, the way it comes across can be similar, which is why we recommend Dr. Xavier Amador's book called
I Am Not Sick I Don't Need Help!. Even though it was written with schizophrenia in mind, the communication tools and approaches may help when the loved one in your life has BPD.
We also have an article on
Anosognosia and Getting a "Borderline" into Therapy, which touches on some similar issues.
How is your relationship with your S33 currently? How about with your GD5?