Hi Hamm, glad you found us and 

20 years is a long time to cope with BPD in a relationship... It's no wonder you sound tired. Have her behaviors and your responses been pretty much the same the whole time? Or have there been times when things were better, or one or both of you were doing something different?
How old are your kids? Are they living at home or elsewhere? And how are they doing with all this?
The whiplash and roller coaster is a lot to live with, for sure. Have either of you ever had a therapist or counselor? Whether she did or does or doesn't, I'd really recommend it for you -- when BPD is in a family system, everyone needs a lot more support. And, therapy/counseling is a good place to get a "reality check" on things you remember, or odd circumstances, or replaying conflicts, or finding new paths forward besides the old conflict "ruts".
Looking forward to learning more of your story;
kells76