What does he get upset about when the friends are around? Do they have disagreements about what they want to play? It could
also be overwhelming to have "friends" over and he doesn't know how to handle this new social interaction. How old is he?
When friends come over, maybe they should only be able to
stay a short period of time (1 hour) and set a timer. That way, he
is aware of how long the friend will be there and he will also be prepared for when the friend needs to leave. If he handles it well, then you can add more time each time a friend comes over. (an incentive) When a friend is coming over, try to get an ETA on when they will arrive and "try" to explain to your son that people need time to get ready and also deal with traffic to get to your house.
My NT "social" daughter is 10 and my Aspie son is 9. My daughter has always been social but in the begining when she started to have friends over, things never worked well. She had to learn that friends don't always agree with what she wants to do. (play/toys) As she got more mature, she's learned that it is
give and take. My son is still learning how to "give and take" and
he hates when he can't do ONLY what he wants to do. I find that he will play 1 thing (like xbox) and his friend will play with something else. I rather they play together but as long as he has a friend over, it's a start. He only has 2 friends that he plays with at school and he has been friends with them for 2 years now.