Just had a big chat with him and he said he often feels left out, doesn't know how to start conversations and feels he doesn't have many friends.
All classic AS stuff. I don't know how to help him. All I could think, and say as he's quite a mature 15 yo, was that social situations are something that he will always find hard.
Academically, he's doing very well and is very driven regarding his studying and exams.
I just hate seeing him upset.