Also, keep in mind that whatever you did to help with the end of your marriage to this woman, it takes two to make it work. She divorced you which means that she no longer has the right to make you feel badly about anything. What happened in your marriage is over. Move on and quit feeling guilty. There’s no going back to change it now and why would you want to?
You are the only one who knows what kind of parent you are or could be. If you are not given the opportunity to see what kind of parent you are, she can not prove the claim of you being a bad parent. She presumably has a new life and husband and she needs to move on also. Next time she reminds you of the reasons she divorced you, tell her thank you, that you are glad she did because now you can do this…and hang up or walk away. Do not let the conversations (arguements) return to your marriage and your divorce. What happened in your marriage and the reasons you divorced have nothing to do with the child and serve no purpose bringing up any longer.
I will warn you that for the first couple times that you do this, and it does take practice, she will likely be very angry. Keep in mind that if it’s not about the child(ren), you do not have to speak with her. If she wants to talk to you, make sure to steer the conversations towards the child(ren). If the only thing that you allow her to discuss with you is the child (children) then maybe some of the decisions about them will be discussed with you first. If you quit paying for 1/2 of everything because it was not agreed on prior, maybe that too will get some decisions run by you.
You have to make a stand, I agree with that. But make if for your child, not against her.