If there is a prior order for parenting time, then that order is still in full force and effect until the modification is accepted by the court.
If not, then no you don't have to let him see the child. However, you're going to put yourself in a SERIOUSLY bad position with the court, especially if he is retaining counsel. If his attorney is any good, should you go forward with your plan, he will file a suit to modify custody because clearly you are not fit to be the primary parent by using your child as a pawn.
Grow up and stop playing games with your child.
Edit:
So Dad creates a volatile environment, but yet you were fine with him seeing his son before? He's the cause of all this turmoil, so instead of seeking supervised visitation, you're modifying child support? Yea...keep talking cause your story falls apart the more you respond.
Edit 2:
So in other words, he's had ADHD since before this modification process occurred and there was not a problem then with Dad, but now you have a problem since he may possibly contest everything that you want because he doesn't believe it to be in the best interest of his child?
So in response to hiring an attorney, you're going to deny him access to his child?
Stop trying to use ADHD as a crutch to further your agenda. A child does not have to be diagnosed with ADHD in order to be manipulated, that happens all the time. From what I've read here, and I'm sure I'm in concert with other readers as well in thinking, YOU are actually more of a harm to this child than Dad is as well as the one who is trying to manipulate the child as well.