As for the support your child is entitled to.... YES, do go through with the forms. Most states - it is mandatory when you file for divorce... just automatic. You don't mention how old your son is, but child support is to carry them through until they are 18, and out of high school. Your son is entitled to it, and it is his father's responsibility! No matter if he is an A, or a druggie, no matter... the boy is due that, period.
IF nothing else, it's on record, and when you file for divorce, if the other parent hasn't paid child support it does count against them. So, joint custody might not be an option for the dad either. BTW... the IRS doesn't look kindly upon deadbeat parents either.