Thank you for the thoughtful responses. Regrettably, validation makes him much worse which seems to be a paradoxical response.
His illness is under control, and isn't life threatening (a blood disorder). He was given a number of completely wrong diagnoses which sounded scary so it's understandable that he now mistrusts the doctors. I don't trust them either! If you ever get a diagnosis of MDS, keep digging and cross reference a 23andme type genetic profile.
And I know what you mean about needing an intelligent therapist; we've known a number of bright psychologists and psychiatrists over the many years but it's obvious BPDh hasn't been motivated to work toward sustainable growth.
He has made a number of attempts to work through his childhood trauma. His father was an NFL player who obviously has the concussive syndrome CTE we're hearing about so much these days. Apparently he learned early on it was acceptable to rage incoherently.
The most disturbing things lately are his out of pattern accusations that I "want him dead" or am trying to "poison" him. My late sister was poisoned by her husband so maybe that's rumbling around the subconscious? Such ramblings do damp down my urge to be the super helper, that is the one who likes to be liked and approved of. (alcoholic mother here).
In the early days I used to tell him that he was quote using his phony mental illness as a weapon. He can be so "non" for extended periods that it does seem like he's faking the crazy as a way to be manipulative. He probably is. There were other names for this condition before borderline but they'd be beeped out by the mods,

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Thanks again for the support and insight!