Dealing with a difficult ex can be very discouraging, frustrating and defeating. If there are children involved we feel it is our responsibility to try to have a healthy relationship with our ex for their sake. At times, your efforts to co-parent civilly may not be returned, hence the frustration.
If your ex makes you want to pull your hair out or, run screaming maybe it's a combination of the two of you and how you interact with each other. Learning some new skills for resolving conflict might be all that is needing in your situation.
Then again, maybe your ex is incapable of respecting boundaries or caring about the welfare of his/her children. If you divorced someone who seems hell-bent on making your life miserable then you need to learn how to deal with a toxic ex who can't police their impulse or need to constantly stir the pot and cause friction.