We don't "own" other people, other people will want to be their own person, do things they want to do, believe what they want to believe. This girl has outgrown you, wants to experience other connections. You should stop trying to pull her back or control her. Instead you would benefit from meeting others and making new connections yourself.

Sometimes after experiencing other connections a person may realize what they did not appreciate about an earlier relationship. That too is not anything you can force on anyone. If you hang around depressed, it won't fix her or what you are experiencing. It's better to move on and make other connections where you can grow instead.