Hi, and welcome! I'll answer your questions below, with my thoughts. I base this on my own experience, and reading the posts and advice on this site, FWIW.
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My questions for the group are:
1) Have you found that people can improve long term with the right meds, therapy, and self awareness? Or, will this "up and down" always be the new normal to some extent.
2) For those of you who did see improvement in their BPD spouse's behavior, were you able to regain trust and connection again? How?
3) At what point (when there is no physical abuse) is it safer/healthier for the kids to have their parents separate then to always be around 1 parent who is mentally unstable?
Thanks in advance to anyone who took the time to read this lengthy post and may have advice.
1) I think the meds really only moderate the extremes; they can make the depressive periods less "low" and keep the person more functional - assuming they work. In theory they may curb some of the angry outbursts, but they also might not do much. Therapy is really the key to actually improving, and the person themselves has to want to go and want to do the work. There's nothing you can do here in terms of getting them to therapy. If they go because of an ultimatum from you, or peer pressure, I think you'll find that they do the bare minimum to get through the therapy sessions and then refuse to keep going.
2) Not to be negative, but I've been on this site for several years, and I don't think I've ever read an account of someone who was borderline (BPD), or BPD with comorbid conditions like Narcissistic personality disorder or Bi-polar disorder actually improve. The statistics are not good here. Hope for the best, but plan for the most likely outcome.
3) This is a hard call. I had heard from several people that fighting in front of the kids is really bad for them. My parents didn't fight very much, but I remember that when they did, it made everything awkward and you could feel everyone in the house suffer from the tension and anger.
I had given BPDxw an ultimatum here that we needed to stop fighting & insulting me in front of our daughter. I wasn't going to tolerate her behaving like that in front of our daughter. Well... that didn't do much. She simply couldn't control herself, and would come up with all sorts of ridiculous excuses for why it was okay for her to do that.
I looked at #3 two ways:
First, if I divorced, I couldn't control how my ex-wife would behave in front of our daughter. But I also couldn't control my ex-wife - by that I mean limit the fighting to shield our D from it - if I stayed married. But if I divorced, at least I could control the environment when she was with me. So my calculation was that if I stayed married, I was exposing my Daughter to the conflict of our marriage 100% of the time. But if I divorced, I'd get (at a minimum) custody of close to 40% of the time. So at least she'd get to live in a "normal" house during the time she was with me, and we could relax and enjoy eachother's company without the threat of BPDxw screaming at her or I.
Second, I considered that if I stayed married, I was modeling an unhealthy relationship for my Daughter, i.e. that it was "normal" to be treated like BPDxw treated me. I was tolerating it. And I read that often the children blamed the non-BPD parent for enabling it.
Again, I couldn't stop BPDxw from getting in a new relationship and behaving like that all over again, but at least I could show my daughter that
I wasn't going to tolerate it, and she shouldn't either, and there were consequences (divorce) for when a spouse couldn't respect the other.
It's not an easy call, especially since my daughter was young at the time, and not able to stand up for herself. It was hard to leave her, but like I said, the fighting was just intolerable for me. I have a friend who's a psychiatrist and I confided a lot of this in him, and he basically said "just get out of the relationship; it's always hard on kids, but in some ways, it's easier when they're young." That sort of clarity was helpful.
So I weighed a lot of the evidence myself before I made the decision, and also spoke with an attorney about my concerns and the likely outcome.
I did not discuss this with BPDxw in any way shape or form, because the trust between had been completely destroyed by this time. I could not have any sort of honest discussion with her. She was too paranoid, insecure, and reactive.