I am a firm believer that it is the control, or lack of it, that fuels the bitterness. He is being told to pay the money.
I have my sone more than mom, and pay $780 per month. I can't really afford the custody but I have good grounds, and may still lose. Your ex probably has little to go on. The attorney is probably feeding his frenzy..remember, if he does not fight then they don't make money.
I am sure you will be fine...just stresses the heck out of ya.