There was a Seinfeld TV show episode about the “preemptive breakup” in which Kramer suggested to George that he break up with the woman he was seeing that he believed was about to break up with him… I think you just saw that play out in real life for you… In real life, with adults, there is no relationship score as to who broke up with who. There are only people who are either together as a couple and those that for some reason are not. The end result is the same no matter who pulled the trigger on ending the relationship. In most cases people unconsciously telegraph their intentions about important issues to them before they actually consciously communicate their intent. I suspect your ex read the situation and somehow tried to do a 180 degree turn - Turning ex’s infidelity into your “trust issues”.