Your brother is Mattheo Riddle. He cares for you obviously, you have the brother and sister relationship. He annoys you, you annoy him. You both mess with each-other. He doesn’t care if your drinking or if you smoke, if your partying with your friends (most likely pansy) because he does the same. He just cares because you’re his brother. You know all his friends because your all in the same grade and all go to Hogwarts together, plus are all in the same house, as well as pansy. She’s friends with all of them. So your all in the same friend group, have been since first year of hogwarts, and your all good friends.