My wife of 20+ years had a year-long affair. She was flirting with starting another one when I discovered the first... When I discovered it, she threatened s****de and has multiple times since... In the most recent one, I had to call the s****de hotline... She had no problem telling me she loved me during the affair, however, so I have a really tough time buying that...
Suicide threats might fit into two general categories, at least my impression. One is that the person is in real mental distress to the point of extreme self-harm. However the other category is the person is making such threats in self defense (due to looking bad) or in manipulation or coercion attempts (distract you from taking effective action).
My primary goal is to do whatever it takes for the kids' best outcome, above my own. She's normally a good mom, but I fear the type of lowlife men she'd bring around my daughters if I weren't there. I can't tolerate the thought of not protecting my kids from exposure to random, strange dudes. As a result, I'm choosing to absorb the pain of it all for now.
Your children are grown and adults or nearly so. Whatever legal authority as a parent that you have now will soon be gone once the last of your children turns 18. And should you decide to end the marriage, your children could, as adults, choose to live with you for now.
Yes, you can't and shouldn't cut them off, you will always be their parent. On the other hand, ponder what example you're providing them. Is the infidelity and all the lies being minimized or addressed out in the open? Will this be a learning experience for them so they learn from you what is acceptable and what is the basis for your subsequent decisions?
I'm not sure I could recover from the infidelity or the BPD stress by themselves...
Can/will she get better? Can/will I? Is salvation possible? What will it take?
"Should I stay or should I go now...?" I fear I already know the answer.
There's no simple answer. No two people, especially disordered ones, are exactly alike. Traits vary from person to person, often described as being on a spectrum or range from one extreme to the other. But there are common patterns and also typical outcomes. One is that we can't "fix" someone else. We can only work on ourselves and even then only reach a measure of success. Our traits are stubborn ones!
Will she reach a measure of recovery and change? Maybe, if she applies herself. That would be an uphill struggle for her. But you're both adults. You have a right to follow your own boundaries of behavior, just as she does. Speaking of boundaries... Boundaries cannot be enforced upon others. So what boundaries really are is how we
respond to poor behavior. Here is a link to a few Boundaries articles and more on our
Tools and Skills Workshops board.
Others here will soon respond with more observations.