Oh, Dekt - that's awful, for both YOU and her.
The fact that you have been able to differentiate between the condition and the 'real' her is extraordinarily mature and insightful, not many people would be able to deal with the instability and still be able to pick themselves up afterwards and continue on - you must have a very strong sense of self and also a deep well of love for her.
Her reaction to your other children sounds very BPD - to her, if you can divide your love and attention with others, you couldn't possibly love her 100%...so all the insecurities creep in and she thinks she will be rejected, so she will firstly attack you (because she feels she is being betrayed) and secondly, 'split' (ie, look at them as either all good or all bad) against the children - she will see them as the source of the problem. It's so, so sad because there are never any winners in this situation, particularly if she is not self aware. If only she could remember what you HAVE done, all the times you WERE there...and put it into perspective. But that is the nature of the beast: The BPD person has a void that needs to be filled at all costs.
I have always known something wasn't right. Always. It wasn't until I got older and started to see the behaviour of others and then compared my own that I found a huge disparity.
I was with my husband for 17 years (until 5 years ago, when we separated) and I treated him, on occasion, deplorably. I repeated both toxic behaviours I had learned from family growing up plus the inherit BPD characteristics - good times were REALLY good, but the bad times were REALLY bad.
I was improving though, bit by bit. I was learning, discovering, seeing therapists, trying to make sense of what was happening, trying to make it right and I think this one of the reasons why we stayed together for so long - he could, like you and your partner, see my behaviour was not ME, but a reaction.
He was patient, didn't try to reason with me when I was having an episode, gave me space to let it vent and boil over...and then held me and reassured me when the shame and guilt set in after I was back to normal. He forgave me and we tried to move on and for that, I will be forever grateful.
Plus he loved having a wife that could do anything she set her mind to, so he could sit back and let me run the show without effort, as long as he showed me the love and affection I needed desperately. And this is what lead us to breaking up - I was changing for the better and started to move beyond just needing his affection, I needed him to step up and look after us as a husband and father, but he couldn't do it. It was just not his personality and we got into such a series of terrible situations because he failed to take responsibility that I decided to leave, for my children's sake as much as my own.
Which was very fortuitous, because 3 years later my daughter dropped the bombshell that he had molested her and now he is in jail, my daughter developed (I think) full blown BPD from the trauma plus she has been diagnosed with Disassociative Disorder and because she cannot confront him, has decided to use me as a scapegoat. Although she had my genetics, she showed no sign of BPD until after she revealed what had happened and the PTSD set in. I watched her deteriorate into this broken, angry shell of her former self, to which she remains today.
So this is why I am wary of involving other people - I would rather cut off a finger than deliberately hurt or manipulate another person, yet I still do by my very nature. No matter how hard I try, no matter how much I read books, speak to people, watch youtube, practice activities - you name it- this hideous thing sits on my shoulder like Poe's crow and bides its time until the next person I develop feelings for. Then it pounces, poisoning my self esteem and starting the road to self sabotage.
Some days I wonder if it is even RIGHT to look for someone out there, knowing I am like this? I mean, if you have a contagious deadly disease, you don't just go around sharing it??!!
I often feel like this in my case - my disease just can't be seen by the naked eye, but can still prove just as destructive.
Thank you for your honest and open post - you have the fortitude of a titan to have survived what has happened and still take time and understanding to reach out to someone struggling here on this forum. (heartfelt virtual hug)
I really hope things turn around for you and your children.