These situations are so tough. There are three things that put me in the camp of just telling him. 1. Pelican's post. 2. You are worried that your ah might say something to someone else and that your son my hear something at school. That would be so awful for him. 3. The incident at the volleyball game. If he is aware of the undercurrent (and he probably is) telling him the real deal might actually be a relief. Kids awfulize and have big imaginations. If he is acting out in uncharacteristic ways and can't articulate why, he's struggling IMO.