Crashing social circles

He's 8 now and has had a great year in Grade 2/3 split class. His teacher was great, his EA super and awesome set of classmates, who were helpful, kind and patient with him. But yesterday, the second last day of this year, my son got a taste of what, unbeknownst to him, awaits him when he returns to school in Grade 3/4 split.
For the first time ever, he encountered a situation that left him feeling deeply hurt and sobbing just because a set of his former "awesome" female classmates decided to "transform into the dark side."
Well, to tell you the bits and pieces of the story my husband and I cobbled out of him at the end of the school day when he was still teary-eyed from the incident, he caught a classmate crying her eyes out at recess and as two other girls surrounded her in a protective circle, he heard the first girl tell the other two that her aunt died recently. My son felt sad for her and offered his sympathy by encouraging the sobbing girl to talk more about it by asking if her aunt went to heaven. His attempt was crushed by the girl's two friends who told him in no uncertain terms to buzz off and not to bother the girl. Heartbroken at being shooed away unceremoniously, my son retained the feeling for the rest of the day. My husband and I could see the total confusion on his face at what happened. He trodded on the invisible circle the two girls were trying to envelope their weeping friend and as he blundered on, he got hurt.
The incident highlighted for me how many social blunders he might be charged with next year by the same sweet girls who he used to regard as friends in Grade 1 and 2. Now, he and his classmates are getting older and circles will be formed and he might often find himself outside those close-knit social groups. Is he getting more vulnerable now than ever to bullying? I hope not. We'll see.