I hate living with my roommate
Why do you feel that way living with your roommate?
At the beginning it was okay, but now he always opens my emails.
It's understandable that you'd be upset about him going through your private things. You should try talking to him first before moving out. If you still can't work things out it might be better to just move out.
Maybe I shouldn't be so upset with him? What if I have gotten so used to it that I like him opening my emails now?
It's better to keep your things private for security reasons. If they can't respect your privacy it might be better to find a roommate who can.