Hi punkertron,
Sadly, many of us can imagine your situation all too well. As you say, it is devastating and disorienting. The post breakup transformation to a seemingly completely different person, with relationships, preferences, values - everything that constituted the person who you thought you knew turned upside down. You've expressed it here so powerfully, and I for one certainly relate.
I loved this person enormously. I genuinely believed she was my soulmate, the person I would spend the rest of my life with. And I wasn't alone in believing that. Everyone around us knew how deeply in love I was. Everyone knew how much I adored her, how proudly I celebrated her, how much I encouraged her ambitions and how fiercely I supported her through everything life threw at us.
I gave that relationship everything I knew how to give, sometimes more than I realistically had to give, because I believed in her, I believed in us, and I believed that whatever difficulties we faced, we would face them together.
Not everyone has the capacity to love and support another person, to enter into a genuine partnership with another person. You should feel proud that you do, and did.
I was devastated when the person I thought was a loving partner dedicated to our shared values and shared life together - and who I had supported personally and financially through multiple mental health crises and other issues - cheated on me with a mutual friend, tried to gaslight me, kicked me out of our shared home, financially mistreated me, unaccountably spent funds that had been allocated for charitable purposes, handed over some of my belongings to the control of his affair partner, and through carelessness, caused the loss of the ashes of my beloved childhood pet (!).
It was not a good experience.
Less than a year later, I am living a very different life - freer and more fulfilled. I could never have experienced this with uBPDx-partner in tow. Sometimes I am exhilarated, overwhelmed even, by how much joy and experience this world contains. The intelligence and clarity with which you write leads me to believe this might be in store for you, as well.