My son is also 13 and I think a comment he made the other day may give some insight. He was feeling very frustrated with his friends and thinking that maybe he'd be happier without friends. Except ... from a short period last year where he had a falling out with his friends he learned that if you don't have friends, you don't get left alone. Middle school kids go after the loner. If you have friends, any friends, you are more likely to be left alone.
So ... even if your son doesn't really want to have friends, if he can get together with some other loner kids and create the appearance of having friends, it will help. I realize that isn't nearly as simple as it sounds, but I thought my son's comment about what happens as soon as you are perceived as being on your own was quite interesting.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).