Hi Tsunami Sailor,
like that name . Be careful as Tsunamis

tend to be overwhelming and are generally not considered safe to sail.
Last week, she felt too sick to go to our weekly therapy session, so I went solo. Our counselor suggested I read about BPD.
Looks like you have a counselor that has a clue. Keep going and if possible keep your wife going too. Couple sessions are generally not the best (too stressful for the pwBPD). If there is an opportunity some time to disengage and let her go alone consider taking it.
What makes this a perfect storm is that she exhibits depressive symptoms often, which she attributes to the loss of her father (who was ill for most of his life) when she was in her young 30s, plus the death of a child from her previous marriage which was caused by medical staff shortly after birth. She is now in her later 40s and in the past year or so has begun symptoms of perimenopause. If that wasn't enough, she experiences body aches and pains, and exhaustion that go along with a diagnosis of fibromyalgia.
You understand her problems well and that is good to a degree. But these are also her problems and she got to deal with them. You can't fix her depression, only she can. Dealing with someone often down and crying sucks . Generally there is not so much you can do - respecting her emotional swings as they come and some gentle validation once in a while (see e.g.
https://bpdfamily.com/message_board/index.php?topic=81442.0).
It doesn't seem too uncommon that sometimes I'm wonderful and sometimes I'm a bastard that she wished she'd never met because I'm selfish and unloving.
Makes you wish for boring grey, this black and white painting can be exhausting . Try to avoid arguing against it - that would be invalidating and will make matters worse. Acknowledge that she thinks you are a disaster (see validation - vocalizing that she (and not you) is thinking this helps a bit to push it out of your head.) and move on to the next task at hand.
My kids don't need to hear the nasty things she yells at me, and don't need to hear the nasty things she yells at them. My kids do benefit from her in her calm and loving state. My kids do need a loving mom. Unfortunately, I wish my kids could grow up without this kind of relationship serving as a model for them.
Emotional instability is never good for kids. Educate yourself about
boundaries (see workshops) and once you are clear where you need them and how you go about them bring about some change.
I don't know if or when our therapist will also talk to her about BPD symptoms. I do know that after 6 months of therapy, she still does not yet own any of her behavior. She understands she shouldn't lash out, but none of that would happen if I understood menopause better, or fibromyalgia better, if I really loved her, or if we moved, or built a she-shed, or if I bought her a camper to travel with her dog, or a houseboat so she could take water vacations with her dying dog, or we followed any of her quick-fix solutions. There always seems to be one quick fix solution in her mind that I politely try to resist by suggesting that her recovery needs to be internal. I am sure this group already knows that her response is to lash out at my selfishness, and that she might as well die... and on and on.
This is not a cognitive problem but an emotional regulation problem. Understanding her condition and accepting it won't bring about change. Therapeutic exercises and a supportive environment (supportive can also mean at times playing hardball) can make a difference. It is hard to restore love. It is possible to restore respect (boundaries workshops) and understanding (validation workshops). If it works it is still a long process.
I try to keep an eye toward doing things for myself. Sometimes those things are good enough for me, but sometimes they are used against me, such as the fact I carve out time to exercise and she doesn't have the discipline (and refuses to take my lead in doing it together).
Good for you that you are keeping some things for yourself. Now she may feel abandoned (again see validation) but that is her problem. Anything that strengthens the identity as an individual of you and her is helping to prevent further enmeshment.
Hang in there, it can get better. Validation and boundaries once adopted can be true energy savers.
Welcome,
a0