You've gotten a lot of well thought out and valuable advice in regards to your post on bullying.
I wanted to suggest something for you to consider that I didn't want buried in that thread. The more you write about your DS and his father, the more I think you should look into Asperger Syndrome as a possibility for your DS's difficulties. A couple of posters alluded to this condition as a possible antecent to your son's problems in school.
IRL I moderate a support and information forum for parents and professionals who deal with children with this high functioning form of autism. I get at least a letter a day from a parent with a story just like yours looking for answers.
FWIW, you have described an classic presentation of a child "on spectrum"- socially inept, lousy at sports, ostracized and bullied by peers who "get" that they're different, drawn to adults rather than peers, blurting random inappropriate things. I could go on.
But the deal breaker, and the reason I am posting this, is your ex. Kids who are diagnosed often have at family member who is likely on spectrum as well. Often that family member is "dad". Your description of dad- totally focused on himslef at the expense of his son, flitting from one special interest to another, an ex-husband- that all fits Aspergers as well.
Obviously, I am not a doctor nor have I met your family, but I do think there are enough clues in your post to suggest you find someone who is an expert to help you.
It's entirely possible that other things could be playing into this- he could have Aspergers and have ADHD, or be gifted, or learning disabled, or have Tourette's. In fact he could have all, none or some of these things. Only a full evaluation will sort this out. I would encourage you to approach the school about and request one in writing. You also might want to have him evaluated privately.
The approach of switching schools is an option, but the bottom line is you can't buy acceptance by paying tuition at a private school. If your son has behaviors that are stigmatizing at one school, they will be at another school. There are therapies and social skills programs that can make a tremendous difference in a child's ability to understand and be accepted socially by his peers.
My own DS got a dx of AS/LD/ADHD back in kindie. Today he's in high school where he's a talented musician; he's also active in the local scout troop and will likely make Eagle in about a year. He has friends, he's no more bullied than the next kid (I watch his facebook page like a hawk, as well as those of certain peers who can't be trusted to behave) and he's happy.
This would not have been possible without the support he gets at school. In middle school he got specialized instruction around organizing his work and writing. He also has had social skills support since first grade to help him blend in with the expectations of aults and peers. We've also provided some private therapy to deal with his level of anxiety, but not all kids need this.