Hi unrequitedBPD,
Welcome to BPD family
First of all, the journey you have just been through to get yourself therapy, your subsequent diagnosis, acceptance of the diagnosis and drive to get ongoing treatment takes a really mature person to do so. It's a really big thing and you should be mighty proud of yourself.

. Not all people with BPD can make this step.
I just want to let you know you are not alone. My Dear Husband (DH) was once diagnosed with BPD 6 years ago and it only took him a couple of years to completely recover with a formal doctor's certificate to prove it. But I have been with him for over 10 years and as his partner, I should know, more than anyone, if he really is recovered. And I can proudly say “yes, he is”, however, it was a lot of hard work. He no longer has split thinking, nor any of the other BPD traits that appeared just a few months into my relationship with him. Like many people with BPD, he is a beautiful, smart person. There are so many different ways BPD appears in people and I am lucky he is a person with BPD who accepted something was wrong with him.
Acceptance of the diagnosis was his biggest step towards recovery and then regular therapy sessions after it lead to full recovery. Although many therapists (T's) will inform you unless they assess the patient for themselves they can not conclude diagnosis.
While that may be true, all of my DH's T's over the years helped him to understand his mother better because she was his trigger's for some of his BPD behaviours, some of them life threatening. At times, I was pulled aside and cross-examined separately to ensure that everything he was telling them was exact. I understood later that this was because some people with BPD can be compulsive liars, but in my husband's case, they confirmed he was honest and did not have the BPD lying traits (of which I understand is more linked with those BPD sufferers that also have NPD).
They concluded that, her behaviours exposed enough traits to agree his mother must have BPD and NPD traits too. Because my DH's life was at risk as a result of they way she treated him, part of his therapy was to understand his mother's BPD & NPD behaviours better so he could accept she is a sick person so as not to allow himself to get upset with her or allow her to make him feel bad about himself.
How he got his BPD also came into therapy, especially once he had recovered and we were planning on raising children. Parenting techniques were raised in T to ensure that my DH did not repeat the same intergenerational parenting techniques that proved to be so toxic to my DH during his childhood as well as his T's really helped him to overcome the emotional and verbal abuse he received by his mother (due to her BPD & NPD) and verbal, emotional and physical abuse by his father (NPD). I know this because I was actively involved and largely present in his T sessions.
How one get's BPD is debatable. I am aware that there are parents out there that did not contribute to BPD diagnosis's in their child, but in my husbands case, his T's have no doubt, it came from his parents ill mental health and treatment towards him. Though he did have some sessions to help him understand not to 'blame' them as they too are victims of dysfunctional parenting in their own childhood.
Much of the things you have spoken about your mother remind me of my mother in law (MIL) and late sister in law. Seeing your therapist should be able to help you at least better understand your mother better.
Your in the right place here. There is so much support and resources and opportunities to connect with like minded people as well as avenues to vent. You mentioned you listened to a pod cast that helped you understand BPD better, many people on this site have read 'Stop Treading on Eggshells'. I have it, it's great, but there are also so many other books and free resources on this website too.
I wish you luck with your journey to recovery. Remember it does take hard work and don't get upset with yourself if you take some stumbles along they way. During these times, I and DH's T's always had to remind DH how far he had come and the odd time he took 2 steps forward one step back was to be expected. It also helped my husband to understand how many different combinations of BPD there is out there because at times, he didn't like being labelled with the same mental health disorder as his mother because she has very hurtful and manipulating traits.