Its good to think of far as of marriage. But if you are a teen, don't worry about it right now. No one going to take away your girl friend from you. Remove negative thoughts from your head. Instead think how, where you will for the next date? How you will propose her? etc. Think bit by bit. plan Bit by bit.
God love his every child. Believe in him and do what you do. He will always be with you.