Why did she blame me for everything?

She staged everything and blamed me for years.
For six years she was the sweetest person I knew. Then suddenly everything changed. She became cruel disrespectful angry and every conversation somehow ended with me being blamed for something. Then she would turn around and complain that I wasn’t replying or communicating enough. What was I supposed to say when every conversation ended with me being made to feel like the problem?
Looking back I feel like every fight was carefully pushed until I became exhausted enough to walk away. Even the friendships with other guys started to make sense later. It felt like she was slowly creating distance between us so I would eventually be the one to end things while she was already having those playful intimate conversations with someone else.
I carried the guilt of breaking up with her for years. Then I found the conversations with that same person. A few weeks after our breakup she announced their engagement and now they're married.
Suddenly so many things from that last year started making sense. I could never understand why she had become so angry jealous unstable and suicidal when she had never been that way during our six years together. I spent years thinking I had destroyed something good only to eventually find out there was so much happening behind my back that I never knew about.