If there's something that you feel you must take, compromise with him. Be friendly (Act as if). Show him how mature you can be in the face of adversity.
If he wants to act like a 6 year old, let him. But don't sink to his level.
It's not a contest to see who can get what... unless you allow it to become a contest.
The material things are replaceable. Plus, the things you leave behind might end up being reminders of you for him.
