There was no 'legal document'. That's why the dude is brain dead. Blindly agreeing to anything from an ex-whatever is dumb.
Oh sure baby, I'll give you my extra key to my car and house just in case of emergency. Oh yeah, I'll just give you my credit cards just in case also. Just promise you won't let your new boyfriend know about this, okay?
Next, a woman has already 'stole' someones sperm. She gave his 'oral favors', saved the sperm, was inseminated by it, and the guy had to pay child support.
Not trying to sound callous. Yes, the laws are not exactly unpreferential to fathers. But, the guy in the linked article sounds to gnikcuf stupid to make enough money that 20% of his wages afford $1,500 in child support. He sounds like he works at the mall or McD's.