I moved in with my GF who is now my wife when I was 20 y/o, five years later we just made our 3 year wedding anniversary in April.
I learned quickly that alot of things change after you move in. You'll have your personal possessions like TV's, computers, ect., but for the most part, everything is "ours" now. Also personal space is a must. If you two think moving in with each other means you'll get closer, you're wrong, you never appreciate freedom until you lost it. So give each other some free time to do hobbies, ect.