Oh OP, I feel for you. My DS is 11 and was diagnosed with ADHD and ASD last year.
In his first school he was written off as a naughty and disruptive child. I spent many tearful meetings in the heads office asking them to help me investigate any additional needs and all they would say to me was that he was just naughty.
He had no friends, no play dates, no invitations, parents actively avoided me in the playground. He would cry and cling to my leg and scream that he didn't want to go in. He nearly got expelled for throwing a chair at a teacher after a meltdown and they still told me he was just naughty.
We moved area for work and he started at a new school, within a week the SEN coordinator called me up and said she wanted a chat. They set him up with social skills lessons (ILLI I think they call it) and carefully managed who he sits next to, let him have a comfort cushion to carry around and hug, removed him from situations where he got overwhelmed and supported us through his diagnosis. He's still an autistic kid, but he's a happy autistic kid with good friends who whilst they might not understand his nuances they see the kind, funny and clever boy underneath.
A couple of things that helped us:
Keep play dates in calm neutral territory, a park or a quiet playground. DS couldn't stand people in his space and he was too intense for other peoples houses.
Don't let him get hyper attached to just one friend, my DS would put all his ADHD hyper focus on one child and it would be too much. We have to manage the amount of contact.
Talk to other parents. As daunting as it seems at first, explain to them that your DS has his quirks. Most people are kind and will understand.
Give your DS a hobby outside of school that he can hyper focus on. Mine has discovered photography and is now bloody good at it! Gives him something to both hyper focus on and be artistic about which calms him down. He can also talk the cows to death about it which gives him something interesting to talk to his friends about.
I really do feel for you, I remember the pain of sitting in the playground by myself just waiting for the "Mrs Flumpalot... can we have a chat?" and feeling like no one got my lovely boy but me. It can and will get better.