Ask a Psychiatrist and Get Answers to Mental Health Questions ASAP
He is still dealing with the news and what the change means to him (loss of friends, familiarity, his school/teachers) Change is anxiety provoking. Even though you're explaining the reasons to him for the move, he is resorting to emotionally reacting (anger, frustration, defiance) instead of the logic behind what you're telling him.
Try to target his emotional side. If possible, take him to the new area and new school for a visit. Explore together what the neighborhood offers, ask him to help you with finding a house, grocery store, etc in the new area.
You can share the things you will miss after your move to the new place (your own friends, co workers, etc) Change can be exciting once he gets over his apprehension. Of course, it would help if your ex remains positive about the situation and encouraging instead of triggering him.
Let your son know that he can still keep in touch w/ his friends via phone, mail, internet/Skype and that he would be able to make new friends and explore new things. Explain to him that life is about change whether he wants it or not. Everything changes and at times it offers positive things (those you've already spoken to him about)
For the time being, try to get him as involved with the move as possible. If you have relocation guides/newspapers etc. about the new area, involve him in learning and telling you what is available there, what things he would like to do and what places to visit. If the area has any amusement parks, bowling alleys, karate clubs, etc. let him make a list of the things he would like to check out. Reassure him that you're available to talk about how he feels, that you accept his anger and sadness and that you do care about his reaction.