He knows the key in his head. So if I delete it he will just re-install and put the key in.
Decapitate him, then. You shouldn't give your ID to anyone. It's what identifies you. If you give it out to someone, sooner or later, your "Friend" will have given it out to someone else, making it difficult to play online (Disconnecting every few minutes).
Grumpy is right. Got a spare email that you can trustfully rely on? If not, make one. I'm not sure you can register multiple keys with one email. You can do chores for money. Maybe throw a yard sale. If you aren't 18 yet, you're better off just mailing it. Just be careful, I suggest you don't use coins. You could also tell your "Friend" 's parents about the situation and they might do something about it.
I hope you get your key back.