On the flip side of the coin, we've all read and heard about the results of bullying for some... suicide. I'm not being dramatic here, it's a real result.
Please consider removing him from this stressful environment. I'm not even saying to homeschool, but I would never send him back into that hornets nest, wolves den, whatever you want to call it. A different school would at least give him a fresh start. BUT, I honestly do think homeschooling for a while is the best route, to allow him time to heal, gain confidence, and get away from a horrible environment. Bullying doesn't make people stronger, it makes them jump out of windows.