How the hell can people just slam the door on a new family, a new life? How do people just quit?
Traggy, her ability to start a new life -- as though she is simply throwing a switch in her mind -- is not a sign of her strength
but, rather, her fragility
. Whereas a normal person has the strength to confront the hurt and work through the issues, a BPDer is so filled with self hatred and shame (from childhood) that she finds it far too painful and frightening to do that. Instead, her mind protects her from seeing too much of reality by projecting all sorts of evil intent and shortcomings onto you.
As I said earlier, this projection works beautifully to protect her fragile ego because it is done subconsciously -- thus allowing her conscious mind to be fully convinced that the outrageous projections are true. In this way, she will run about slandering you with vindictive accusations -- and do so guilt-free because she consciously believes the irrational nonsense coming out of her mouth. Of course, this is why BPDers rely so heavily on projection to shelter themselves from seeing too much of reality. It is guilt-free.
She does it with such calm and happiness that she is leaving me in her wake that I just can not fathom what I did to her for this to partake.
You likely did nothing at all to cause it. As I just explained, it does not matter WHAT you do. When a BPDer decides to leave you, they will protect their fragile egos by projecting all sorts of demonic attributes and evil intent onto you. Unlike us "Nons," BPDers are able to do this projection so easily because they have always had great difficulty with "object constancy."
That is, a BPDer has great difficulty perceiving you as being essentially the same man from day to day. You've seen that in the way your W, in only ten seconds, can flip from adoring you to hating you. Her subconscious therefore finds it to be a cakewalk to project all sorts of bad features and thoughts onto you. It is what a BPDer does so very very well.
This ability to flip from one intense feeling about you to its polar opposite -- called "splitting" -- is why a BPDer's feelings are both intense and shallow. This is why a BPDer's feelings are said to be "a mile wide and an inch deep."