If i received cash aid and am now married to the''absent parent'' is he still required to pay child support?

i have two sons one is from my fiance,and the other is from a previous relationship.i began getting cash aid when my second son was born but i only wanted it for myself and my oldest son,i was told i couldnt pick and choose so i had receive aid for both kids.my fiance has been supporting both since day 1 and now 3 years later they are sending us complaints and summons for him to pay child support for my youngest son.is he required to pay child support if we are married and he is supporting the child?