TOL:
One of your messages in your comment deserves repeating, and some emphasis on it would benefit many.
You noted that aside from the stigma that accompanies a diagnosis and medication, there are countless situations of people who are unable to sustain the challenges of marriage that have no psychiatric labels, have not been subjected to evaluation, and are not taking any medication or therapy intervention. This is responsible for a great many broken marriages. In the Torah world, we tend to refer to this category as having poor midos. And you seem to imply that poor midos might be a characterological situation that will not be affected much by regular reading or studying of sifrei mussar. I soundly agree with you. That is why the homework done prior to a shidduch needs to address the matter of personality. The kinds of questions worth asking include, “How does this shidduch prospect handle stress? What do they do when they get angry? How do they deal with confrontation? How do they manage under pressure?” Responses to questions such as these (providing they are honest) are far more relevant than the individual’s academic record. All marriages will entail challenge. Is there a foundation of character traits that can deal with this? Or are we assuming that things will just work out (e.g. because the boy is a learning boy)?
You alluded to the book “Walking on Eggshells”. Fine book, useful content. Still, living with a spouse that has BPD is a huge undertaking. Kol hakavod to someone that wishes to stick it out. Many do that, and they are praiseworthy. Others jump ship, and often face a lifetime of challenge, nastiness, battles in court, and other forms of suffering. There are other books, too, that are worth checking out. I take a position that BPD is incurable. It can be managed in many cases, but a lifetime of intervention and support is needed. I am witness to cases that entered treatment, improved greatly, but upon stopping therapy, reverted back to their old ways. What Marsha Linehan contributed with her development of DBT was a set of skills that the person could continue to use without continued outside help. Once again, a cheaper way of continuing what therapy would accomplish. Saves lots of money, and provides a helpful strategy to maintain stability. But the condition of BPD never leaves; it just continues to be treated.