"Borderline" is a very confusing thing to call it. The name came from when doctors were only starting to classify mental illnesses, and they pretty much lumped people into two groups. Psychotic being if people are out of touch with reality - delusions, hallucinations, etc. Neurotic being those who are in touch with reality but have depression, anxiety, .... There were some who didn't seem to fit clearly in either group, and they decided to call those Borderline. That concept was passed down and is where "Borderline Personality Disorder" comes from - the name, anyway. Because there is depression, anxiety, mood disurbance, as well as some disconnection from reality at times.

You can read more about BPD here: http://psychcentral.com/lib/2007/sym...lity-disorder/

Addiction and self-destructive behaviors are often part of BPD, and depression and anxiety can be related to it. Some of the sympmtoms of PTSD can overlap with BPD. Nothing is really cut and dry, but symptoms related to a specific traumatic event are more likely to be PTSD, while the way that you learn to interact with people and approach the world, possibly related to a lot of emotional invalidation and difficulty being understood (or understanding yourself) during childhood is more likely to be expressed as BPD.