When she gets upset she dominates, everything I say is interpreted as interrupting her, and we talk in circles for hours or days. It's exhausting
Part of a "non-BPD-person's" initial response to what is irrational behavior is to try to use logic and their own point of view to mitigate the situation. Sadly, this is the worst thing to do once a person with BPD or another "emotional-disability" has lost their limited emotional control. Defending your point of view, your actions, or intentions is invalidating. Invalidating a pwBPD is seen as attacking them, and sometimes even a small issue, like who said what can hit them in their very core of their being. BPD is about shame avoidance. Things that you or I may not find shameful, like being corrected about say a date on a calendar, can be shame-inducing for a pwBPD because they cannot handle being wrong. If they are wrong once, then they are wrong now, always and forever, and that must be avoided at all costs, even to the point of horrible rage-arguments, re-writing history, and blameshifting.
Their feelings NOW are their feelings at all times - past feelings no longer exist, future feelings are no consideration. If they are happy with you NOW, they are happy. If they are mad at you now and FEEL that you are a hateful, mean, wrong person, then you always have been that and will always be that (until the storm passes and their emotions "reset".
Once of the biggest things, you CAN do, is look at the lessons, especially about how to stop making things worse. Our initial, instinctive reactions DO make things worse. We want to explain, to fix, to soothe, and all of those actions, especially past the BPD breaking point, are invalidating, which hurts the pwBPD, and ramps up the emotional drive to be right.
You can use the tools to defuse some conflict and to learn how to deal with conflict that you were not able to avoid. One of the biggest things to realize is that this is part of the person you love, just as much as a heart condition, diabetes, or a physical disability would be. It will not go away 100%. There will always be times when it will pop up - BUT, after being on this site for many years, and working on my own co-dependency issues, our relationship is a lot less volatile than it used to be, and we are going on 20 years now.
You, as the "non" will have to accept certain levels of responsibility that your emotionally disabled wife cannot. You will have to learn what you will and won't accept, and set some boundaries within yourself for how to deal when things try to bypass them. Some boundaries are shared with the pwBPD, some are internal. I never told H about BPD, other than to talk about my parents and coping with being a childhood abuse survivor. I never let him know I apply those same tools to him, and that he exhibits to a lesser degree many of the same behaviors they did. It would not help, it would make things worse. Very few with BPD can handle being told even by a professional that they show signs of it. Instead, it's best to sue the tools to help YOU, to keep you strong, to determine what battles are worth fighting, when to validate and when to simply ignore things. I try to separate the behavior from the man as much as I can so that the comments made during a fight don't hurt as badly. He is what he is, and he is a man I love who has an emotional disability and cannot manage himself like you'd expect an adult to do at all times.