Maybe not a total exit. I have money coming in that my wife does not know about. I have a date to move out when she is at a conference. I will try to get an apartment as soon as the check clears, and hopefully I can make it all work. I do have a separate bank account that she does not know about. She does not know about my plan to move out.
My "plan" is to tell her that it is a separation, not a divorce. And to see a marriage counselor and see if things can get repaired, though I think odds are quite low. If they do not work out, I hope that it will smooth the transition.
I will also be talking with a high-conflict attorney this week (again, when the check clears).
I would suggest you consult or interview attorneys first, of course
privately and confidentially as with your other preparations. Then you can ponder the legal advice, cautions and strategies. They will know the local laws, processes, courts and likely outcomes far better than you. You may get a sense with one that you would be more comfortable and served better. You don't have to hire (retain) the first one you meet.
Speaking of separation is perfectly fine and appropriate. The last thing you want is a huge incident. Stair stepping into it is wise.
My plan after moving out was to be home when she got here and tell her. I was going to have a friend drive me and be ready to drive me away. Am I still being too nice? What if I just called her on the phone as she was driving home? I think being there in-person is the right way to do it, but bottom line is that I do not want to do it.
It is commonly said that the highest risks of DV, claimed DV or an incident/conflict are during or soon after separation. You can control your actions, reactions and overreactions but the ex likely can't or won't. It is wise to have someone nearby and available for support (or rescue) since pwBPD might restrain themselves, somewhat, if they realize they're not in a private scenario.
In some rare cases members decided it was so dicey they let the court's process server deliver the notice of divorce proceedings. As noted by PeteWitsend, no matter how nicely you intend to approach it, it likely won't go well. So Goal #1 is to protect yourself both in the moment and later with the legal processes.
Be ready to exit promptly, especially if the situation unravels or police are threatened. There is little benefit to stay in the moment and JADE (Justify, Argue, Defend, Explain). Later on you can arrange times and places to discuss details and development when the other might be calmer. (Before, during and even after my separation & divorce I recorded our "interactions" - quietly and on the down-low - just in case so I would document that I wasn't the one behaving badly or aggressively. My ex knew how to pose as a "victim".)
Please don't have such discussions while either one of you is driving a vehicle. The roads demand full attention.
I am hoping that if she agrees to the therapist, that I will be able to tell the therapist about the problems with her there. I have tried to tell her about her trauma problems a number of times, and she has not been able to hear it.
There is a possibility that suggesting a therapist might in itself trigger her. Many pwBPD are in Denial and either refuse or soon quit therapy efforts.
Also, one common goal of marriage counselors is to repair the marriage. It appears you've concluded that the marriage can't be repaired sufficiently for you to stay. However, being willing to involve therapists or counselors is a good start at the beginning. Who knows? As unrealistic as it seems, she might benefit from the therapy approach even when the marriage will end.