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Does anyone have any advice on how to handle this situation? Do I advocate for DBT for my son simply out of its value vs. HIS black and white thinking? Do I mention possible BPD to the psychotherapist / counselor working with us (without telling my wife)? Do I wait 2 years until she is less split black on me and then tell her?
My gut tells me that the order I put those in goes from good to worse... but perspectives are welcome.
Two things:
First, regarding getting therapy for your son, this shouldn't be an issue in divorce. Courts view counseling for minors favorably, and will order it, almost on request. The challenge is ensuring the BPD parent goes along with this and doesn't try to sabotage the counseling (for whatever paranoid or insane reason they claim is an issue).
In my case, BPDxw actually suggested getting a therapist for our daughter shortly after I filed for divorce. my concern was that BPDxw would keep changing our daughter's therapist until she found one that she could control & would go along with her nonsense. what we did was have a child psychologist my attorney knew vet a list of respectable therapists in our area, and allow BPDxw to pick from that list. And we had the order drafted that neither parent could change counselors without the other's consent. On that specific point, there's an argument you can make that it's important the child develop trust with the counselor, so that prevents the BPD parent from changing whenever they feel like it.
It went as I could've predicted. From our list, BPDxw chose the male therapist closest to her house (she always told me she could get men to do what she wanted easier than women). She took our D to a couple sessions, and then when she realized he wasn't going to let her sway him or go along with any ridiculous accusations she was trying to make, declared that therapy for our daughter was a waste of time, she was "fine" and she wasn't going to take her anymore. She also apparently got in a fight with the therapist when she demanded a refund for a session she paid for and cancelled and didn't get the refund as soon as she wanted. LOL. As he told me this, I was like "Haha, now you see what I've been dealing with."
One thing I didn't foresee was the therapist retiring... our decree didn't account for that. Make sure you have a plan in place to account for that. Maybe the therapist designates a successor, or something.
In practice, I've found it's not easy in practice to arrange therapy, especially if, as I do, you don't get custody until classes end for the day, and that makes it challenging to get the child to therapy during normal business hours. The number of therapists with evenings or weekends open is small, and I also found a lot of therapists don't want to see kids who's parents are actively suing eachother out of fear of getting dragged into it.
Second, as far as telling the therapist your concerns goes, I think any good therapist would ask the parents their concerns and be fully candid here. If your wife is BPD, as well as ADHD, I would stop relying on her for anything or worry about getting her consent. Your focus and priority is your children, and her concerns - even assuming she's able to be honest about them - is a distant second to your children's needs.
Stay strong. You might even want to mention to the counselor that your STBDxw has been diagnosed with ADHD, and has been in therapy herself. Stick to the facts in this, and the therapist should realize to discount (if not completely ignore) her complaints or comments on account of her existing issues.
You can't go wrong by advocating fairly for your son and being honest. Don't worry about appearing biased if the things you are saying are factual.