A biological father is the father of the child. A step-father is not. If the step-father has legally adopted the child that is not his when married then yes, he would have to pay support. If not married and the child is not his then no, he does not have to pay child support, but he may have to go to court to resolve the matter.
In general, child support ends when: the obligor has legal custody of the child; the child is deceased; the child has been adopted; the child is emancipated (i.e., self-sufficient); the child has...
Yes, when either the mother or the state department of revenue files a complaint for child support against him. The court will issue an order that can include back support.