I have no such fear. Once I really solidified into who I am today, I realized a few things.
One of those things was that Karma has no BEARING on whether or not my future wife will cheat or not. My mindset, and my mindset's hold on my woman controls that. So, with that perspective, it doesn't matter what I do or with whom because my woman won't cheat on me.
The reason why these women cheat is because a) their dude is FAR from Alpha and b) he is not the 'best option' and she knows it...she is basically settling. I am both Alpha AND the best option, therefore they would be CRAZY to jeapordize any dealings with me.
At the lights of your ex, does that change ?
Yes...it can be postulated that she is indeed crazy.
...or was temporarily insane at best.