Thank you for starting this discussion thread.
I'm not aware of specific fiction books celebrating friendships.
I've personally gravitated towards towards thoughtful movies, and TV-series' that have celebrated friendships esp. from novel, quirky, funny, and even intellectual perspectives e.g., this sounds like a terrific TV series from Britain that would be a popular PBS-TV series here in the States; which might resonate with people on the Autism Spectrum.
Anyways, I'm not aware of specific fiction that has "struck-a-chord" so to speak - If such fiction truly "struck a chord," I personally, would probably get that boost of confidence to develop, and maintain friendships...esp. with like-minded people who also enjoy PBS TV broadcasts that celebrate friendships; which might include characters on the Autism Spectrum.