I think those observations are indeed a common trend you will see when reading through the posts on this forum.
1. When they are triggerred (e.g., by any slightest disagreements, physical separation due to personal travels, etc) and split afterwards, they then behave as multiple different personalities?
Personnally, the way I see the "multiple different personalities", and keep in mind I am not a mental health expert, only the daughter of a BPD mother, is that it might be linked to the arrested development they suffered when they were abused/traumatized.
My mother can act both like a teenager and a little girl, but seldom act like a healthy adult.
When triggered, and depending who is facing her, she can be either waif, witch or queen.
If it's a child : she is witch, and will rage strongly enough to become physically abusive.
The silent treatment I associate with the Queen, her default when dealing with an adult.
When we try to make her view how she also hurt us, then it's waif.
So yes, it comes accross as multiple personnalities. Have you read yet in the borderline types? Waif, hermit, queen and witch? I see those as a spectrum within which BPD oscillate, as opposed to a type they always display.
2. When they split, their emotions are so intense that they cannot reason like a normal, healthy adults? Even if they try to "reason" it would be purely based on emotions and they refuse to see the reality as it is (e.g., accusing that you are leaving them even if you have no intentions to do so and assure them you will stay with them)?
Yes, and as I understand it, this also affect how they recall something. My mother once accused me of having been ungrateful, despite me remembering quite clearly that I said thank you. But on the moment, she was dysregulated and jealous and looking for any small slights to blame me for her own pain. She wasn't perceiving me, just how I was making her feel, and she had to justify it somehow. So she blamed it on the fact that I was ungrateful for everything she did for me... Which wasn't even close to reality.
I don't think it was malignant. I think she truly doesn't recall it the same way I do. And I think her memory can change depending on on present emotion too... Reality and her story, for her, is never clear and arrested... Hence her lack of self, or poor sense of self.
3. They shut down after a disagreement - regardless whether they intend to punish you or they intend to shut down their emotions which are intense and uncomfortable?
Can you clarify what you mean by "shutting down"? Like a depression state or what we often refer to as the silent treatment?
4. Not only are their close relationships (romantic or platonic) unstable, but their life choices as well? For example, they chronically sabotage their own life goals and careers?
Yes, although this could be observed in a variety of way. My mother wouldn't see it as self-sabotage, to her, she just got tired of it and changed. She could have made a lot of money from a business she created, but sold it to one of my cousin that had money issue, and got mad when he started missing paiement, etc. For some reason, she never put two and two together that she made a bad business decision, despite other people giving her better ideas, like having employees... To her: she wanted to move in another city, and needed to sell! There was no convincing her otherwise...so of all the potential buyers, she chose the most troublesome one.
She changed career many times indeed, and always move from one house to another...
It is as if, when staying still, she starts blaming her surroundings for her state of pain. So she moves away, or changes it brutally, without waiting for the best opportunity. It simply has to be NOW, else she will burst.
Then the pattern repeat.
It does cause hardship, but not always either, sometimes it works... Which is why I don't think it is self sabotage.. they are just very impulsive.
