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But here’s another big red flag - she has been reading a book about open relationships, and I think that is validating for her, and where her language about me being brainwashed by society came from. The red flag is that the woman she is interested in pointed to her book. So while W claims the other woman is not trying to break up our marriage, clearly that is bit the case.
pwBPD can be very good at co-opting political and social issues and verbiage, as well as popular wisdom and sayings to justify their own actions and selfishness.
You have to ignore this, and fight through attempts by the pwBPD to use them to warp your own values and relationship; you have to have some fortitude and stay firm. It's easier to stay balanced then, and not get swayed by some of this nonsense.
For example, "
I'm reading this book and it says open relationships are totally normal."
You "
Maybe they are, and I'm not judging anyone who's in them, but it's not something I want for us or something I'm comfortable with."
...And at this point, you'd be well within reason to end the discussion; no need to justify your position. Closed relationships are also totally normal! Did you enter into marriage with the stipulation that she was allowed to have lovers on the side? It doesn't sound like it from your posts, e.g. her saying that her bisexuality was in her past. So why even entertain this when it goes against your values?
Like everything else in their lives, I think pwBPD's political and social views are very shallow and always self-serving. In my experience, BPDxw was (according to her) "very feministic" ... but of course, only when it suited her. She preferred to work with men and if it came down to hiring a woman or a man for something, she'd always hire the male or prefer to work with the male because according to her, she could manipulate men better than women. When I had interactions with people she worked with, she was always cold to the other women and had a bunch of excuses why they didn't like her and why she couldn't stand them.
And it was wrong for men to cheat... except when she learned an acquaintance she was feuding with was cheated on, in which case, I remember her defending the cheater and claiming the woman deserved it.
And so on for everything else in her life... religion, politics, etc. She was never consistent in any of this, and it's really a hodge-podge of left/right issues with no consistent ethic, and no moral compass guiding her, other than "how could this benefit me right now?"
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I’m also learning this woman is basically homeless, yet has a job in the medical field. This feels very suspicious and guaranteed drama.
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Be careful here... I would not sleep on this issue. Figure out more about this person and what their goals are. You have kids together! What kind of drama could this expose them to? Your wife's "needs" - I put that in quotes, because wanting to have an affair is not a need - come in second to them.