Paying child support to the mother of my son.

My ex and I were never married. We make roughly the same income. We have joint physical and joint legal custody. Our son spends more than 50% of the time with me and attends the school district that my residence is located in, not her's. She has claimed him every single year since he was born on her taxes, and despite my suggestion to have an every other year deal to be equal, she refuses. She is now taking me to court for child support. I've already been paying her a hefty amount monthly to help out, but she apparently doesn't think it is enough. I am a very good father. A much better and more responsible parent for my child than her. I don't know where to turn because any information I find is directed in the mother's favor and there is such a stereotype that the fathers should be paying the mothers. I am not asking for any support from her, nor would I ever. I simply don't understand why, if I am a more present parent in my child's life, that I would have to pay her.