morning, bit hangoverish.
aupair sorry no help here.
franca yes I'd say it is quite common and complicated. true when there's three it's not easy to handle and one always ends up paying the price. In primary school it happened to me. I was always invited by these two girls and made to be the maid while they were the princesses or smthing. I still remember to this day the playdates, the house, the anger inside, the cliques in the playground etc. IME the only resolution is to step away and find friends one is more compatible with. but this is up to ds when he is ready and when it happens. i wouldn;t know what you can do about it but reassure him and advice him. maybe gently push him towards other friends?