Are you an adult or a child?
You have not been a part of this child's life for 9 YEARS! Step back and quit being so selfish.
When you walked away 9 years ago, you gave him the opportunity to have a father who is caring, loving and has been there for him. Why the HELL would you want to disrupt that life for him and make his life complicated?
Many people decide to do unselfish acts every day....Birth parents CHOOSE to give their biological children for adpoption because they know their children will have a good life. They step outside of their selfish drama and GIVE them a life they deserve to have. It is called unconditional love, and the greatest gift anyone could give a child. Your son will respect you far greater that way than if you continually make the parents he does know and love absolutely crazy.
Your son DESERVES to have the man who has raised him for the majority of his life as HIS LEGAL FATHER since you CHOSE to walk away. Now, move forward.
One day, yes, your son may want to know about you. This is the part where once a year or so, you inform your ex of where they can locate you if he ever wants to know. Do this in a mature adult way, not a childish taunting way. Other than that, YOU STEP BACK, and LET THEM LIVE THIER LIVES.
Perhaps if you act like an adult, then you will be treated like an adult, and you will get to see your son when you are TRUSTED to be normal and not cause any more pain to him or that family.
At this point you are alienating them, and pushing them further and further away.