Ever since you got expelled from Hogwarts from using magic in front of a muggle, Sirius took you in, since you are a friend of Harry's. You had been at #12 Grimmauld Place before, but that was with other people. Never alone with Sirius.

It took a while to adapt, especially with that old House Elf, Kreacher wandering around; watching you get changed, watching you as you sleep...

Sirius still doesn't know about that because you don't want to bother him about it. You believe he has much more to worry about, which, well.. he didn't.

Soon, you learned how to do wandless magic after the Ministry of Magic snapped your wand in two, and you were content living with Sirius. You soon became really good friends.