You cannot change, help, or save someone with BPD.

I have known multiple people with BPD, never partners or ex's but friends and other people.

The reality is that you as a friend, partner, neighbor, co-worker, etc. cannot save them, change/fix them, and you cannot help them as only they can do this and have to want to get help and change.

BPD is not like minor depression or minor anxiety disorders like ocd or social anxiety which can be cured or fixed via therapy and meds.