I agree with Dottie and Gratified. This decision is really yours.
I suspect that your son doesn't want to leave his friends in the same way that kids that age don't want to give away their old clothes and toys, even though they don't work for them anymore. They don't understand that change is sometimes necessary to find a better fit, and that once you have new things, you wonder why you ever held on to the old ones.
Is there any way to dip a toe into new friendships at the new school? Could you get together for a playdate with someone from there? Or visit at recess?
I suspect that if he finds a better friendship fit, he'll be fine with the transition.
Remember that these friends are all he knows. As bad as the fit is, it's the only thing he's got. It's pretty normal that he might resist change. That doesn't mean change shouldn't come though.
Best wishes. These decisions are so hard on us parents!
