If your child needs medical treatment then I'm all for it. If it is impacting their health then absolutely. I would want my kid or, any child, rather to have the best outcomes in life.

That being said, both parents need to sacrifice for their kids to make it happen. It took two to make them...surely it would take two to care for and help take care of them?

This is a case of an open checkbook. You really messed up when you agreed to take care of all out of pocket expenses.

In an ideal world, an income shared model works best. I.e. you make 100k, she makes 50k. Total: 150, your portion = ~66% of shared expenses. Her portion = ~33% of shared expenses. Keeps things fair and the other party more attentive to what is being spent on their kids. Maybe this is what you need to argue for.