Hi tdbisjl, thank you for posting. I am also married to a wife with BPD. She has recently accepted the diagnosis, after 18 months of couples therapy and years of individual therapy. I also am in therapy for myself, which started when the BPD-related behaviors surfaced 18 months ago. We struggle daily/weekly and I won't pretend to have good answers because I am very much "in the thick of it."
It's great that you are doing some reading. There are a lot of good books and the ones you've chosen are among them.
It is so VERY hard to avoid taking the bait when someone, no matter who it is, tells you that you did/said/didn't do/didn't say something. It can be the most ridiculous falsehood that you could disprove in a heartbeat with all the verifiable proof in the world, in the most loving and calm tone of voice, etc... and you will still be "defensive." It is so freaking hard. Example: a while back my wife told me she had "proof" I was cheating on her with a coworker of mine whom I barely know, because she tracked my phone on google maps and saw that I had driven past the address of this person in the course of doing my job. It was a false accusation born of fear and one that I could easily disprove by showing her both my work schedule and an actual complete route map on Google maps that showed where I was, when I was, every minute of the day...and I was castigated for being "defensive." (Yes, there are lots of issues in this, including that it's not ok to track someone's movements, make up accusations, etc etc...) My point is to say I get it.
Something I have read, perhaps somewhere on bpdcentral.com, is the idea that validating the feeling behind the accusation is not the same as admitting guilt or agreeing with the conclusion. I really struggle with this in practice, but when I am able to do it, it does help and sidesteps the "defensiveness". One of the methods I have had some success with is S.E.T. (from "I hate you, don't leave me" book, I think? I've read so many, they're a jumble).
Here's a link to it: they explain it better than I can
https://www.verywellmind.com/support-empathy-truth-set-for-borderline-personality-425229It's a difficult position to be in. It's hard to be on the receiving end of the result of her enormously painful internal feelings without taking it on, trying to fix it, and allowing it to wreck you. You're taking good steps so far. Keep reaching out on the boards here. The support is wonderful and needed.