Still, I can't take responsibility for more than 50% of my own M's destruction, so I am certainly not going to listen to her nonsense about my possibly having an impact on her third M. She's been "damaged goods" long before I ever came around.
And I'd warrant that your own xW was also somewhat "broke" before you ever knew her. Perhaps? I know no one is perfect, but I am beginning to think that unfaithfulness in a person's makeup doesn't often happen via spontaneous combustion; there's usually something there to begin with, some underlying flaw in their character already.