P.K.
This is one you cannot fix. He will just have to face it head on. Who knows, maybe once she moves he will be forced to make another friend.
Or, maybe he will be a loner all thru school. Not all people are joiners and very social. My husband was painfully shy when we met. Fast forward 38 years and he never stops talking. He talks to everyone!!!!
Can't force your son to be someone he is not. Embrace his shyness. How about martial arts. He does not really have to communicate. Who knows maybe he will be some great inventor because while everyone was just hanging out, he was diligently working on a cure of some kind.