This is something that's still a little difficult to talk about. As a child, Harry had so few people in his corner, and then at age 13, he discovers that he has a long-lost godfather. Who's cool, and interesting, and so what if he just spent over ten years in wizard prison? So anyway, now Harry has a surrogate father figure, which is good for Harry, but bad for Sirius, because Harry's father figures don't have an awesome survival rate. There are two super maddening and tragic things about the untimely death of Sirius Black. The first, and this is not said enough, is that his death is almost entirely Harry's fault. He falls for a predictable Voldemort trap and, rather than contacting Sirius via the special glass that he was given for that exact purpose, he launches a foolhardy rescue mission that Sirius then has to rescue him from. Equally upsetting is the fact that Sirius would not have been killed by that curse alone, if not for the crazy random happenstance of him falling through the veil. The forces of the universe really came together to kill Sirius Black, and we were not at all emotionally prepared for it.