Harry is grieving for Sirius, and he blames everyone, including himself, for Sirius' death. He blames Snape for not making it clear he intends to alert the Order of the Phoenix to check whether Voldemort has, in fact, captured Sirius.
No, it is not Harry's fault that Sirius died, any more than it is Dumbledore's fault or Tonks' fault. Those are the three people who are presented in the book as feeling culpability (Tonks' apparent feeling of guilt was expressed by Hermione).
Why did they mute Harry's scream? They muted Harry's scream when Sirius died because it was so heartbreaking that Helena Bonham Carter (Bellatrix) and Emma Watson (Hermione) cried. It was too sad to watch, so they muted the scream.
He did not wish Sirius' death. He did what he could to protect him. In spite of what Harry chose to believe, Sirius' decision wasn't Severus' fault. Sorry to lose a Member of the Order he would have been - they weren't that many; but it was not a personal loss.
I figure that he was still very upset, losing the last (good) member of his family. But Harry knew he had no time to mourn because the death eaters and Voldemort were still on the loose. And he knew that that was what Sirius would've wanted: him to carry on and finish of Voldemort once and for all.
In the film, Bellatrix hit Sirius with the Killing Curse, Avada Kedavra, killing him before he passes through the Veil. In the book, the curse that hits Sirius is not identified, and his being knocked through the Veil is what causes his death.
There is no doubt that Sirius loves Harry and is fiercely protective of him, but he does let his more immature impulses take over sometimes. In The Order of the Phoenix, Sirius wants to visit his godson in Hogsmeade while disguised in his Animagus form.
Harry Potter: Stag
Harry's patronus is undoubtedly the most recognizable. The stag is first seen in Harry Potter and the Prisoner of Azkaban when it saves Harry and Sirius Black (Gary Oldman) from the dementors at the lake.
Snape tells Harry that he, Snape, is the Half-Blood Prince, and that Harry should not use his own spells on him, as Harry's father did. Harry dares Snape to kill him and calls him a coward once more.
The answer is that Sirius wanted to deflect attention from the real Secret-Keeper. He probably hoped Voldemort would go after him so he could steer attention away from Pettigrew.
Sirius Black
"Come on, you can do better than that!"
The real reason, and the reason why Dumbledore didn't let Harry fall into any wizarding family, was: Dursleys was Harry's only living relative. If Harry lived with them, he would be under a protection charm casted by Dumbledore.
Part of the Second Wizarding War
Voldemort wanting Sybill Trelawney's first prophecy, therefore planting a false vision in Harry Potter's mind in of Sirius Black being tortured in order to lure him to the Department of Mysteries.
Sirius was not proved innocent until after he was killed during the Battle at the Ministry during the summer between Harry's fifth and sixth years. It was proven because the ministry admitted that Harry has not been lying, as well as the fact that Sirius's Will was found.
It is hinted that he has done something that would inspire Harry to seek revenge, but it is not until Christmas that Harry learns that Sirius betrayed Harry's parents to Voldemort, then, when confronted by their friend Peter Pettigrew, killed Pettigrew and twelve incidental Muggles.
In the Harry Potter series, Bellatrix Lestrange used the spell "Avada Kedavra" to kill Sirius Black.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
In the [Deathly Hallows] book, Snape's dying words to Harry were "Look at me". Right then we did not realize the significance of his words but in the very next chapter when Harry goes through Snape's memories in the Pensieve, he comes to know how much Snape loved Lily.
"The first thing Snape asks Harry is "Potter! What would I get if I added powdered root of asphodel to an infusion of wormwood?" According to Victorian Flower Language, asphodel is a type of lily meaning 'My regrets follow you to the grave' and wormwood means 'absence' and also typically symbolised bitter sorrow.
Snape's secrecy is revealed to have been a mask and he has sacrificed being well-liked to be able to save Harry, all because of his love for Harry's dead mother: the only friend Snape ever had.
While in school together, Sirius once tricked Snape into almost entering the Shrieking Shack while Lupin was there, transformed into a werewolf. James realised the danger and stopped Snape, saving his life; this is the incident Dumbledore referred to at the end of the first book.
1 Albatross
As the rarest Patronus in the Wizarding World possible, the Albatross represents an enormous bird that flies freely across any sea. This rare Patronus represents those who are simultaneously fearless, optimistic, happy-go-lucky, and ambitious.
It turns out (naturally) that Sirius was framed, and even after their twelve-year separation he and Lupin remain fiercely devoted to each other. By book 5, the two of them are living together in secret.
So how are Sirius and the Weasleys related? Phineas Nigellus Black is Sirius' great-great-grandfather and Arthur's great-grandfather, making the two men second cousins once removed. (Sirius correctly notes the relationship in Order of the Phoenix.)
Although he was the heir of the House of Black, Sirius disagreed with his family's belief in blood purity and defied tradition when he was Sorted into Gryffindor House instead of Slytherin at Hogwarts School of Witchcraft and Wizardry, which he attended from 1971 to 1978.