Emmmm, Oops
Does he feel worried, or do you? Because it is very normal for a boy of barely 3 to have no special friends. And although he can read, he is still little more than a toddler, emotionally, and therefore isn't capable of making and maintain strong bonds with children his own age, as older children are.
He may look dreadfully lonely, flitting from group to group, but it's normal, honestly, and I would be surprised if he felt at all lonely.
The reason I ask if it is him or you is that he is showing no real signs, as far as I can tell from your messages, of feeling intimidated, but you seem very very anxious for him - understandably because he is your little boy, but perhaps unnecessarily?