Hi, Isolated!
Rev is right. We generally do not recommend bringing up BPD to our loved ones. It rarely (if ever) goes well or is well-received. Have any therapists ever told her of their suspicions?
Ultimatums, in my experience, don't work (and not just with BPD -- I tend to not like ultimatums in general). Either the person will balk (sometimes violently) or they will give in. But it's not a "giving in" that will be productive long-term.
One thing my therapist told me when I was struggling with my H, before he got help: "He has to want to do it. Not for you. Not for your relationship. For himself. That's the only way it will really work." That requires a level of self-awareness and emotional maturity not often found in pwBPD.
So, from what I understand, if your wife does agree to DBT solely because she's desperate to keep you around, the chances of it actually working and her sticking with it past the crisis are slim.
I'm not trying to be defeatist. Just realistic.
If you do choose to deliver the ultimatum, I would urge you to read up on communication techniques like DEARMAN, which can be very useful in talking to pwBPD:
https://bpdfamily.com/message_board/index.php?topic=160566.0The fact that your counselors have been concerned for your physical safety is a big one and one that calls for careful approach and planning.
Without knowing details of your relationship, I'm worried that if you bluntly tell her you're leaving or deliver your ultimatum, it may trigger a rage episode -- one that could be dangerous for one or both of you.
We have a Safety Plan here that I hope you'll look at. It's long, but there's some very valuable information there that can help you manage this in a way that protects you:
https://bpdfamily.com/pdfs/safety-first-dv-1.pdfTelling her in a public place, or with a trusted friend present or with some kind of pre-arranged "safe word text" agreement with a friend or family member might be advisable.
I've thrown a lot at you but I hope you'll take a look. What do you think?