You can't have kids by yourself. Your partner is just as important. Why would it be different when you no longer live together?
I can offer hope and ideas for navigating the most difficult co-parent behaviors. Divorce is hard on everyone, please don't use your former partner as a target for your rage and frustration.
In some twisted way, my ex-wife assumed that she was the better parent and thus more entitled to the child support, the house, and the kids' care and feeding. As a good dad, this was just her assumption. Today, her assumption wound probably be supported by state family law. But, I believe times are changing.
Not a percentage of salary earned. No, she believed, still believes, that the child support is her entitlement. This is no longer a relationship it's just a business contract. I am no longer a person to her, I'm a debtor. I'm the problem. I'm the reason she's unhappy.