R.M.
My advice is to cut your losses and get this creep out of your child's life. He will never act as a father. He has proven that to you. Ask him to relinquish his parental rights so he will not have to pay child support. Yes, you'll have to support your son 100%, but you're going to have to support him anyway. This way you won't be spending thousands of dollars in attorney's fees and having your sweet son dragged back and forth through the court system. Believe me when I say that this will be much less heartache than deaing with this man for life.
Saying you want your son to know his father... do you really? Do you really want his heart to be broken by a man who will make a lifetime of broken promises? Saying a child needs a mother and a father is dreaming at this point. What he needs is a loving mother and a loving father. He does not have a loving father. He is lucky to have you. Concentrate on building the home you want to raise your child in and stop using that energy trying to force someone to be what he has proven that he will never be. You can teach him to grow up into a responsible loving man. He will not get that from his bio-father.