Hey, my friend. I agree with Pei. Dbing him is the way to go.
But, I would add that you should not be talking to his friends about him at all. Not appropriate in my book. And if he ever finds out, it aint gonna be pretty.
It really doesnt serve you well to hear what they say. You dont even know if they are adding to it. It doesnt help you in any way.
It is disrespectful to your son. These are his thoughts to his friends.
As far as he is concerned, you really cant do anything more. He knows you love him. He is just hurting and confused. Add in the hormones and man, it's tough stuff.
Continue to be the kind of dad you want to be. Set your boundaries with him. No disrespecting you. Never a bad word about his mom. Treat him with respect. Let him know you love him.
Then, let this play out for him. In time, he will realize what really happened. Children know way more than we give them credit for.
Time is what is needed. So, be patient. It may take a long while.