I am very sorry for you and your son. My son, who is 12 now, suffered terribly due to bullying a couple of years ago, before we were able to get him into the right school (a school specifically designed for children with ADHD and other behavioral challenges). He became so distraught and anxious about not fitting in at school that he began pulling out his hair on one side of his head, creating a large bald spot.
One thing I have learned by working with my son…children are amazingly resilient and can overcome all sorts of obstacles that seem far more insurmountable to adults. My son has never ceased to amaze me with his ability to make it through what I see as paralyzingly difficult situations, and doing so with incredible grace and consistency.
One positive that can come from a child who struggles with making friends is that, once he/she does find a friend or two that he/she is comfortable with, those friendships usually become very strong and are an extremely emotionally positive experience for the child.
Your son is lucky to have such a caring and dedicated parent as yourself. That alone will help him through these tough times more than anything else.