Never been to court but pay child support

I have a 6 year old son with an ex-girlfriend. We have never been to court and my son lives with her. I take him every other week and have been paying child support of $50/week by check as well as $20/week I have been putting in a college saving mutual Fund. In addition, I have never refused to buy him clothes or anything else she has asked for, but dont have receipts. My question is if I ever go to court will I have to pay arrears if the $50/week amount didnt meet the New York State formula amount. In addition, will I have to pay 17% to this girl for my son even if I am married and have additional children in my current relationship. In addition, she is currently married with another child as well. Also if I go to court do I have to bring my tax return showing my wifes income as well or would it just be based off my W-2, as I dont want to impact my current marriage by dragging in my wife.

Child support would be based upon your income in accord with the state child support formula.

You should maintain good records such that if it ever goes to court you can establish a clear and consistent payment history. If there is no prior court order establishing support, it appears that a New York court has discretion to order child support retroactively to the birth of the child - you want the court to decline to exercise any such discretion by virtue of such factors as your express or tacit agreement as to the amount of support, and your consistent payment history.