That is certainly a bizarre state of affairs, it's a shame you have lost a good friend just because they fell out with someone else - and to avoid them they are avoiding you too.
I can not say I understand the logic, it seems very unfair on you and your son whatever his own feelings are. Sadly if his mind is made up there will be little you can do - such a shame though.
Sometimes decisions are not logical and this time it seems he has a hard time to deal with his emotions. Whatever it is, I hope it will pass. Thanks for the resteem!