What is the process in California for seeking child custody and visitation rights

California Custody/Visitation: i am 17 and I have a son that is 20 months old. His biological father has never paid child support and hasnt had contact with him since he was 5 months old. The Bio father recently turned 18 and my son is on public assistance, therefore the District Attorney stepped in the collect child support. This Bio fathers response to the court papers were, he was not the father and did not want to pay child support. We had to go for a DNA test, which turned out positive. I am recently married to a wonderful man who has taken all responsibility for my child as a father and supporter since my son was 6 months old. Now that the District Attorney is going after the Bio father for child support, he wants to go for custody and visitation. What are my rights as far as custody? Since we were never married, do I have sole custody of my son until the Bio father petitions the court? What grounds do I have to terminate his rights so my husband can adopt him? Please respond with any information possible, please....