This happened to our eldest and it”s hard.
As kids grow their personalities sine through. Ex-best friend is a bully, basically, perhaps the teachers could see that when they split them up.
The other kids will change as well, as kids get older they look at bullying more for what it is.
We had to build up our eldest daily for years.
He needs to look forward not back, his old friends are not very pleasant now, he is just their kick about person to enjoy being horrible to. Play with the girls, go to chess club or dodgeball at lunchtime. It’s a three form a year school, there are other people to hang out with it just might take some time to find them.
And you will have to pick up the pieces if need be every single day. It’s heartbreaking it really is but what choice do you have?
Our eldest is sitting GCSEs in summer, he’s confident, smart, has no time for “roadmen” as they are called. Doesn’t use or has any interest in social media, has a best mate, group in school, had a teenage crush relationship, does sport and volunteers, has a part time job, working towards decent grades, is polite, fun, respectful and applying to colleges, looking to go to uni and with hard work and luck hopefully a meaningful, content, ambitious adult life ahead of him.
In contrast, the youngster met his best mate first day of reception, were never in the same class again, are in different secondary schools and are still bessies, friends stay friends if they want to.
It”s soul crushing, you can’t be happy when your child is sad, all you can do is keep him going, find the good things.
There are lighter days ahead OP.