In my opinion, BPD is essentially chronic core insecurity that manifests and affects many aspects of your day-to-day life, whilst you're under the sheets with the lights off, or partaking in engaging with family relationships over holiday dinner.
I would highly suggest the book Search For The Real Self by James F. Masterson, whom will in a simplistic tone delve into the the capsizing, inhibiting, underdeveloped false self that can be problematic for day-to-day living.