I have to disagree. They like you and you like them. They say they miss you. So go ahead and meet up with his friends. If he has a problem with it, it is his problem, not yours, and not theirs. He needs to learn that he can't control what other people do, he can only be responsible for his own actions and reactions.
Our background raised us in an atmosphere of control freaks and humble servants. It sometimes goes against our nature to not give in to the control freaks, but we really do owe it to ourselves to grow up and move on. Your ex obviously needs to grow up too.
Tammy