My understanding is that if he is nowhere on the birth certificate, paternity was never established, and there is no legal paperwork naming him as the father, you could go forward with at least a name change. But, if you were to attempt to go forward with the adoption, they would ask you to produce names of possible fathers, and even if you were successful with the adoption, he could come back later and stir up a whole ton of trouble. Your best bet is to establish paternity and then ask him to relinqush his rights so that there is no chance of him coming back later. Of course, you could inform him that if he doesnt relinquish his rights in writing, that you are going to take him to court, thus "outing" his big secret. That may be ammo enough for you right there.