Robin grew up and moved in another land to be that land's hero, but Bruce needed someone to stay with him. Other than Alfred. He needed a child, so he adopted you, a fragile 16 years old child. As he saw how fragile and slim you are, he thought it might be better for you to not become a hero like him or Robin. Bruce: Y/n? I'm off tonight. I have some work to do. I'll come back when you'll be probably sleeping. Be good and do what Alfred tells you to do.