N1
My DH can relate to some of what you have ben through. He and his ex split acrimoniously when DSS was 6 months.
His ex has been incredibly manipulative. She openly tells me that she decided she wanted a child and knew DH would make a good dad so told him she was infertile. They split before she knew she was pregnant, they then tried to reconcile but they argued constantly so DH left when DSS was 6 months. He still says that was the hardest decision of his life.
His ex used access as tool to have control over him. If she was in a mood, no access, if she was jealous of him no access.
My DH isn't perfect, he can be grumpy and hard to talk too but he has never let his son down.; He has never played games with access or with his maintence payments. Even when he was made redundant he kept up payment. He may question with me what the money goes on and have a bitch that she never has worked. But he pays regardless. When we got married she got all funny (8 years after the split) and we had no access for 6 months, the same when DS2 was born.
But the money was a given. If she buggered off for the next 6 years and we never saw DSS, DH would still pay the money because it's the right thing to do.
So what if not every penny goes on his child, how can he control that? If it means his DS gets a mother who is slightly stressed as she doesn't have to watch every single penny then good.
OK if DSS was going short of food, heat and clothing then he would take steps, he would look into paying off the gas bill or getting asda vouchers. he would also look into whether his child was being properly cared for. But as it is his basic needs are being met so any money after that he has no say in.
He can't dictate what money goes where. And life is too short to be that petty.
If you want to have the entire upbringing of your child to be one long argument you are going about it the right way. If I were you I would move on from the past.It's happened its over.
All that matters is your child, and at the moment your money games are a contributing factor to the dispute between you and your ex. They may not be the sole problem or the cause but for sure they are making them worse. So you can moan on and on 'but she does this and she left and and blah blah'. But you can't control her actions, only your own. Your child doesn't care she wants her parents to get on.
My DH knows that if the question is ever asked that he can look his son in the eye and say that he played a part in his upbringing as much as he could financially and emotionally. I don't think in all honesty you will be able to on either front.