nosuchdragon, I also have a high-functioning H who is uBPD/uNPD. He has a high-responsibility job. The face he shows to neighbors and his coworkers is a different one he reserves for me alone.
There is a workbook by Lundy Bancroft, a therapist/counselor who deals with abusive relationships entitled, "Should I Stay or Should I Go?" It is a companion book of his, "Why Does He Do That? Inside the Minds of Angry and Controlling Men." Although not specifically addressing BPD or NPD, the book deals with the dynamics of emotional (and also physical) abuse perpetrated by pwBPD.
You might want to read the workbook to help you sort out a decision to leave for good. I am at that point myself.
And, no, you are not alone. I have felt the way you feel numerous time, and sometimes still do. I had to come to the realisation that my H is a very sick man. I have looked at his FOO and all the signs are there.
It's not easy to leave a relationship when the dynamics have a hold of us. If you read this presentation, it talks about the "Jekyll and Hyde" aspect of abusers--just as we know happens in the splitting of pw BPD. It also advises not to attend joint sessions with a spouse as abuse issues are separate from ordinary marital issues.
https://www.ecok.edu/sites/default/files/siteContent/administration/centers-programs/brandon-whitten-institute/Why%20Does%20He%20Do%20That.pdf