I often think of my xabf's ex wife. She had a major freakout and made herself seem utterly crazy. I am absolutely sure that she wasn't taking responsibility for her part through the destruction of their marriage... things like, controlling, judging, anger, etc...
In my mind, 50/50 is correct. I am positive that with your ex A, during the relationship it was probably more like him 10% and you scrambling to do 90%...? but think of it this way... You were giving away 40% of your responsibility to yourself. That 40% was your part that you were missing and could not give as a part of that 50/50, and for us codependents (or those of us that find ourselves in these relationships), taking responsibility for ourselves is exactly the task at hand. Which, btw, is completely different than blame. But because all we can control is ourselves... it is just a matter really of how long it took us to wake up to the fact that nothing was going to change. And for that, we should be forgiving ourselves