I believe she carries deep trauma from being molested by her father and then being blamed by her mother.
It feels like we’re stuck in a cycle where we both get pulled into our own pain, and I don’t know how to stop it.
It was the same for my ex, except it was her stepfather.
With my marriage it was a decade of gradually increasing stresses and triggers, much rooted in her childhood FOO (family of origin). Then I conceived of a not-so-brilliant idea that she would be less distressed if we had a child, you know, a kid discovering the joys of life. Clueless me, I had no idea why it backfired. Eventually, looking back, I suspect in her perceptions I had stopped being a husband but transformed into a father, a huge trigger for her. Within a few years life became impossible and our marriage imploded big time.
While no one knows your future, I would suggest you use caution before contemplating having children together. It could make things worse and certainly vastly more complicated (custody and parenting issues) should the relationship end.
How to stop it? You can improve your communication skills - browse our Tools & Skills workshops board. We strongly encourage therapy as well. However, you've already mentioned she is resistant to acknowledging her issues (as my ex did) and you can't make her start therapy or even apply therapy in her life. People with BPD traits (pwBPD) are known to be resistant to be objective about their own issues, instead Denials, Blaming, and Blame Shifting.
I did try apologizing to my spouse as we approached the end of our marriage. Endlessly. As you have, over and over. After several months I just came out and told her I would apologize - once - and only for what I saw was appropriate for which to apologize. I didn't realize it then, but I had set a Boundary for myself. Um, did I say my marriage failed?