My wife and I made an agreement that we were both happy with and I paid it for about 3 years. She then went to claim something from the state and suddenly the CSA was involved, through no fault of my ex.
I was immediatley in arrears, the money I had paid was discounted as though it never existed and I was in dire straights. Guys committing suicide over the CSA was a regular thing. CSA mail insisting on more money only came on Fridays and you could never get through to them. Unless you lived through it you have no idea of the pressure.
Fortunately for me a good job came along and I took out a loan to pay off all the arrears. The CSA changed the rules and now actively encourage partners to make amicable agreements, as I did in the first place with my ex.
I have always supported my children and they have always got whatever they ask for. But events change. Children grow up and become adulte, their attitudes change and family circumstances change. You can get to a position where you will always love them as your children, but you dont always like what they are becoming as adults.