Hi, there is a lot to unpack here, but I have some thoughts:
I deeply love her as she is, when not "in episode", a wonderful person and a great mom. She also changed me a lot and was by my side in my hardest times when I was diagnosed with diabetes t1 at 35, just couple of months after we met. I have firmly decided to never let her go and always see her for the good in her.
Given that you start here, as well as posting on the "bettering" board, my sense is you want to make things work, for the whole family. To me you sound more hopeful than despondent, and that's good news.
My problem is that my wife has a history of suicide in her family. Her aunt took her own life at 55, shortly after entering menopause. My wife is now 52 and on the edge of menopause. Her parents, while really incredible people, both show some beta cluster traits. Her condition is improving and episodes are more and more rare, now on a monhtly to even bi-monthly basis.
I think it's typical that mental illness can run in families, whether it's because of nature, nurture, environmental factors or some combination. But having said that, you can't say for sure if menopause was a trigger for your aunt, or that it will be for your wife. If your wife isn't feeling well because of perimenopause or the onset of menopause, she could seek medical treatment, and there are numerous treatment options. Personally, I have never felt better than after menopause, though I did experience some age-related issues like trouble sleeping, dry skin/itchiness and emerging thyroid issues. Doctors can and do help, with medications, lifestyle changes and/or supplements. For me, making some tweaks has helped me feel better than ever.
That your wife's behavior is improving signals to me that maybe going through menopause will actually help her feel better and more balanced. At least that was my experience.
During each episode she threathens divorces and spills fire on me, saying that I ruined her, am constantly keeping her in relationship as in a prison, that she hates me an can not stand even looking at me.
PwBPD will often say things they don't really mean when they're dysregulated. The more outrageous, delusional and wacko her accusations are, the more you know that they're not based on logic, but on out-of-control emotions. Has your wife actually taken any actions to pursue a divorce? Has she hired a lawyer? Has she left the home for a few nights? Does it seem she's changing up her life/friends/jobs in preparation to leave you, live independently or live with someone else? My guess is that she has not, because she's bluffing. Now, I don't like being threatened, and I don't like to listen to B.S. either. But my sense is, she's probably mad about something else, like not getting her way or being disappointed, and she's turning around and blaming you.
On these boards you'll see recommendations about how to handle dysregulated behavior, such as not to JADE (Justify, Argue, Defend and Explain), because when your wife is riled up, she can't think straight, let alone hear anything you have to say. I like the Gray Rock technique, which is to be as still, quiet and boring as possible, so as not to engage in a heated argument and feed the fire of her ire. I might slip out of the room or silently do a chore, like taking out the trash, which gives me some separation. If my spouse follows me around, I might say quietly, I have to go to the bathroom. Oftentimes the little break in time and space is enough to end the argument. Basically, I'm giving them an "adult time out," that is, time and space to cool down.
Another approach you might try is reassurance. If she says she wants a divorce, you could say, I love you so much, I don't want a divorce. Maybe she's seeking reassurance, but her BPD thinking is getting in the way of that? Remember, fear of abandonment is a huge trigger for pwBPD. She might feel like she's letting you down, so she tries to beat you to the punch with a threat of divorce, when what she really wants is to know you love her?
Our 15 yo son is always listening from his room and it is surely not good for him. I managed to do "a talk" with him when he was around 13, explaining that "mum has a strange brain with ups and downs, and you should not take it all into your heart". He is now used to it and also nows how to handle her and not put out fire with gasoline.
It sounds like your son knows how to be a Gray Rock. But the situation is concerning, because he might feel that he's to blame for his mom's distress. It's never fun to live in a household that seems to be in constant strife, and ready to explode. The other thing I wonder is if he will think it's OK to scream and make grave threats, modelling himself after his mom's behavior. If he sees his mom gets what she wants by acting out, he might adopt the same tactics. By the same token, I think it might be beneficial that his same-sex parent is the stable one, and my hope would be that he takes more after you and your behaviors than his mom and hers.
Nevertheless, living with an unstable emotional dynamic can be extremely stressful. You might consider getting him therapy, if you think he needs it. He might not right now, but he may need more support in the future.
I guess my recommendation would be to ensure your son has opportunities to experience more "normal" home environments, such as staying with grandparents or cousins for a few days here and there, if that were possible, a little vacation. He might like the idea of a summer camp. Getting involved with positive role models with organizations such as the Boy Scouts might be an option as well. Is he on any sports teams with strong male coaches? That might be an avenue to explore. Eventually, he might consider college campus as a refuge from domestic strife. In the meantime, I'd recommend that you get plenty of one-on-one time with him too. You could bond over something of mutual interest--movies, fishing, paint ball, a Saturday getaway, whatever you both enjoy.