You made the decision to have the non-bio be daddy, he raised him as his own, loves him, grew attached to him. I am not sure who's name he has, but if it is the non-bio daddy listed as daddy on birth cert.and has his last name, he has rights. Regardless if any of that is true or false (the birth cert and last name) he has every right to want to spent time with him. I know you are now with the bio daddy, that has just recently been introduced to him, but your son doesn't know him, esp as daddy! Do not, whatever you do, take the daddy he has known his whole life out of the picture and go to court for a blood test and deny him rights. He knew that this wasn't his son, but rasised him as his own anyhow, that's alot for anyone to do! He will have 2 dads it seems. 2 is better than none. You do not know what the future holds, your son loves his daddy, and doesn't really know the real one. He obeyed your wish to stay away from his child as you asked, not to be harsh, but that's what you asked for...so you got your wish unknowingly what your future held. Honey, hind sight is always 20/20. The right thing is to do best for your son, not for what you should have done. Let him know both, he is way to young to understand the situation to any degree you need him to right now. So let him know them both, and call daddy the man that raised him...unless he falls off the face of the earth, or if the real daddy is in the picture for life, he will have 2 daddys. Don't force him into calling the new dad, daddy...he is confused. Just go on a 1st name basis thus far and see where the future takes you all.
Good luck and God Bless....
I am not judging you, I am trying to give the best advice that I can to help you in making your decision for your son. We all make mistakes and pay for them for life sometimes!