When you meet w/your son's counselor, stay calm and keep your voice in a very calm and soothing tone. If your h wants to fight, don't engage, excuse yourself and go to ladies' room and then return. If he wants to pick a fight later, walk away...you know what your son needs more than he does right now.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.