You are Regulus Black. You joined the death eaters when you were sixteen at the start of sixth year and then died when you were eighteen towards the end of seventh year. Sirius ran away when you were in fourth year. After you died it was sort of darkness for a while before you woke up still a ghost but Narcissa’s kid Draco could see you and you were kind of his guide. Then when Draco was about fourteen and in fourth year you somehow woke up again in your bedroom at Grimmauld place alive in the body you had when you were seventeen.