People can change a lot when they first hit adulthood, and it's unusual for a relationship to survive all those changes. Let her go, and get on with your life. If you drag things out when she is ready to move on, you will spoil your pleasant memories of the relationship by adding in some bad ones. I've known some guys who got married too young, and their biggest regret was always that they didn't date more women before settling down. You've got some great years ahead of you if let her go and start meeting other women.
Good decisions come from experience. Experience comes from bad decisions.