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She also regularly claims that both her individual therapist and our couples therapist have privately validated her narrative and told her that I am problematic. I can’t verify this, and I wasn’t present to represent myself. She had a solo session with our couples therapist and didn’t tell me until the next morning right before our final couples therapy session.
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The second marriage counselor/therapist I saw with my now-XW was a situation where she had been seeing him individually, and told me he said she "was fine" and there's nothing wrong with her. I bet she was fully honest and candid with him...

She then told me he wanted to see us both, and I told her I was concerned about "bias" here and didn't think it was appropriate for us to see her individual therapist as a counselor. She disagreed and told me he did too. So we went to see him a couple times.
These sessions would quickly break down, as she would scream - and I mean scream - once I started talking. I would come prepared with notes about the things that happened during the week that I felt were making our marriage untenable, and once I started talking she would demand I shut up or "just file for divorce already" and things like that. The therapist would sit there quietly and didn't see a problem with this.
Also on our first visit, he mentioned he was writing a book about marriage relations and asked me to help proofread it for him. He sent me like a 300 page PDF. I read a bit of it, and realized it was just the typical "Learn to speak eachother's love language" BS. I thought he was kind of an idiot. I also refused to go back to see him after the second blow up there, because it was actually making our relations more contentious, leading to
even more conflict during the week.
A lot of therapists are just bad; either they're incompetent and/or desperate for clients and are happy to let disordered people come in there and rant, so they can take their money.
In contrast to this, our third therapist was much more professional and started to call my ex-wife out on her subjective takes, inconsistencies, and that sort of thing, which of course enraged BPDxw, and caused her to scream at the therapist on our last visit and refuse to go back.
So I think there's a bit of a Catch-22 when it comes to marriage counseling with a BPD spouse: Either the therapist is incompetent and allows the pwBPD to dominate the sessions, in which case they become pointless exercises of blame-shifting,
or the therapist is competent and zeroes in on the behavioral disorder issue, in which case the pwBPD will panic and refuse to go back, as they realize they will not be able to control the sessions and this may result in them being held accountable for their actions.