I’ll start.
We had great chemistry but different goals. She was religious and looking to marry and thought she could change me, a non-religious person who intends to remain unmarried and childless. I was up front about the lack of religion and the lack of desire for marriage. She was not up front about her intent to change me.
After two months of regular flings she told me we couldn’t see each other anymore, because she wanted someone to go to church with, it was my fault she was living a sinful life (totally), and she was cheating on me with another dude was a Christian.
“Till death do us part” made a lot more sense when most people never made it to 65.
Nowadays, with the over-100 bracket being the fastest growing demographic (albeit from a very small base), the whole idea of monogamy starting in one’s 20s becomes less and less aligned with psychological and social reality.