Post devorce, how often has your ex dumped your child on you?

Its happen once in the beginning in January. About 3 weeks after she told me. Since then I have been doing most of the caring for are child. I did at least 50 percent throughout are marriage and 80 percent now. She keeps telling me she want custody, but had not been acting like it. I am kind of fed up and want to say fuck it. I did not want this, I wanted to fix it, I made mistakes, but so did she. I never understood how father could walk away, but ex wife can be such a pain in the ass and almost leave you with no choice.