Sirius was your godfather. When in the third year you found out with Harry, Hermione and Ron that he was actually innocent and that the one to blame for your parents’ murder was Peter Pettingrew, you didn’t even have time to know him better than he had to hide away. From the third year to the end of the fourth, you got very close via letters; and when finally the summer before the fifth year came, you and your twin harry, the Weasleys and Sirius were all at grimmauld place.