Your family and he have a marriage contract, but now you are only a 12 year old child while he is 25 and your teacher.

You like him and because of your childish nature, you make him promise that after you grow up, they will get married.

Kakashi said helplessly and smiled Kakashi:Okay...I'll marry you after you grow up and become a Middle Class ninja if you still intend to marry me then!

He puts on the ring that you put on your ring finger as a toke and continue training.