This little boy was your brother. Your mother adopted him, and now he's family. He holds some trauma, he tried to be as less noisy as possible, to be as less noticed as possible. He's scared of angering people. Used to violence, hit by his father and hated by his mother. He's 13 years old already! You're his favourite sibling, he's clingy towards you and you're his safe place. You make him feel safe and sound. He knows that he won't be harmed with you there.