Hi Steve,
this is a puzzling question, one which most of us asked ourselves at some point in time.
BPD is to a large extent an emotional regulation issue compounded by splitting. By acting out at home she works though her negative emotions we all have. And splitting allows her to push the negativity and acting out aside and being a very different person on the outside.
We all experience negative emotions - it is just that we usually work though them in a less destructive manner. By allowing her to behave out of bounds at home she is able to show a cleansed side of herself to others. And as long as she can abuse you there will be no reason for her to change. Why should she, her way of life is working well for her. Please read up on
Boundaries in the workshop section.
Speaking of negative emotions:
"The "public" thinks she is the nicest person in the world. How does that work?" Why does it matter to you if your wife looks good outside? Is there a slight sense of envy, a sense of competitiveness on your side? Or a sense dread and isolation of not being understood by others? That would be all ok and it would be natural to feel so. And still this would be another reason to work through boundaries as that will be helpful to focus yourself on your side of the story alone. Not because your side is the only one that matters but because your side is the only one which you can control. You can't control her. You can't control other's view of her. You may be able to influence both a little with a large expense of energy. But you have full control of yourself and there is a lot more power than you realize.
I am not doing well. I am at a loss. I know what I should do but the truth is I am afraid of the consequences. I am trying very hard to take care of myself.
Any change will have consequences.
Any continuation without change will also have consequences. Likely you need to make a few bigger changes. Together it may be a huge change. Now here is a secret: A set of small changes can add up. Small changes enable bigger changes. Bigger changes add up. The first ones are the hardest, it gets easier after a while.
Hang in there