but I never think I will fully really understand how someone can just write you out of their life so easily after 19 years - not wanting to remember a single thing - and how they can move on like you never existed.
That's what honestly hurts the most. That you meant nothing. Blame their sickness or don't, that is just an awful way to deal with someone you "Love". I almost refuse to see it as anything but illness... . that they can't even respond to an email, a letter, a phone call. I just do not have words for it.
I remember having a brief two week relationship with a woman. I slept with her once, and talked with her a few times afterwards but admittedly dropped her flat and went no contact. She went ballistic on me, and deservedly so. After about three days, I wrote her an email and called and apologized for my awful behavior. I was absolutely guilt-ridden. We are now friends, on Facebook no less - but what I'm saying here is that this how normal, healthy people deal with relationships. They recognize the error of their ways and find some resolve and closure. People with BPD CAN'T do that.
Please take solace in the fact that your life will be more rewarding and fulfilling then their lives will ever be. Count on it. You will grow from this, whereas they will continue to spiral out of control and crash over and over again unless they somehow find the will to get better.