Yes. Snape was a triple agent which by definition is a traitor.
Although it seems like an act of betrayal, Snape kills Dumbledore simply because the elder asked him to, when the opportunity came.
However, near the climax of the book, Snape leaves Harry his dying thoughts (to be viewed in the Pensieve) and ultimately reveals to Harry that he had been loyal to Albus Dumbledore throughout the series.
One of the biggest twists in the entire Harry Potter franchise came when it was revealed that after years of torment and bullying, Severus Snape was a triple agent: he was working for Dumbledore while pretending to work for Voldemort and telling Voldemort he was pretending to work for Dumbledore.
Severus Snape killed Hogwarts Headmaster Albus Dumbledore because he had been asked to do so by Dumbledore himself. Dumbledore found out about Draco's task to kill him and so asked Snape to do it instead.
Voldemort trusts Snape because he's good at his job as a double spy and as an Occlumens. Voldemort is so conceited that he probably just doesn't expect Snape could be a better Occlumens than he is a Legilimens.
Voldemort did get to know about Snape's betrayal. Harry himself tells him right before their final showdown. This is their final dialogue: "I brought about the death of Albus Dumbledore!"
He doesn't trust Snape as Dumbledore does, but he believes that he can detect any disloyalty. Moreover, Voldemort regards Snape as highly intelligent and therefore ' as a true Slytherin ' a person whose top priority is to take care of himself. To his twisted mind, selfless equals stupid.
Warner Bros. Severus Snape is one of the most divisive characters in the entire "Harry Potter" series. He was a double agent, so many character details were kept a secret. His mother was a witch and his father was a Muggle, leading to the moniker "The Half-Blood Prince."
As Rowling explained in a series of tweets, Snape loved Harry's mother, Lily, and his unrequited affection drove him to resent Harry's father, James — and by extension, Harry himself.
Now, as firmly established, Snape was not the greatest fan of Harry, but that didn't mean that he ever stopped loving Lily. Dumbledore was surprised that Snape seemed to care for the boy. With a swish of his wand, Snape conjured up a Patronus – Lily's Patronus, a doe. 'Always,' he said.
Gaunt's ring
After retrieving the ring Albus Dumbledore himself fell victim to a curse that, even when contained, would likely have killed him within the year. Once rendered defunct as a Horcrux, the stone was placed inside a Golden Snitch and left to Harry Potter in Dumbledore's will.
Voldemort told Snape he had been a faithful servant, but that he had to regrettably kill him, as he mistakenly believed he was the master of the Elder Wand, as Snape had killed Albus Dumbledore, its former owner the year prior, during the Battle of the Astronomy Tower.
Do you think Snape cried once he was alone after killing Dumbledore? Yes, without question. Despite Dumbledore's manipulation of him, Severus was fond of the old man, even though at times he was annoyed as hell at him.
The acclaimed author explained that Harry paid tribute to Snape because of “forgiveness and gratitude.” Though Snape bullied Harry, he also saved him. “Harry hoped in his heart that he too would be forgiven.
Snape was torn. He 'loved' Harry in a way due to Lilly but every time he saw him he was reminded of his feelings for Lilly and Lilly's feelings for James. He also seemed to find Harry reminded him of his father whom was someone Snape hated. Hence he probably did not like Harry either.
He said, "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 symbolizes bitter sorrow." If you combined that, Snape's words mean "I bitterly regret Lily's death."
It was after Voldemort threatened Lily that Snape left the cause (we see the exact conversation in 'The Prince's Tale,' the one that takes place on a stormy hillside). Her death solidified his resolve with the Order of the Phoenix, but it was the threat that made him leave the Death Eaters (sort of).
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
As a result, both of them were mistaken. With the return of his Death Eaters at the end of Book Four, Voldemort declared that Snape had left their ranks forever. Conversely, Dumbledore went on declaring his undying trust in Snape. So Dumbledore was no more wrong than was Voldemort.
When Snape heard the prophecy and pleaded with Voldemort to spare Lily's life, he may have inadvertently caused his downfall. While we know Voldemort killed Lily, he did give her a choice. If she stepped aside and allowed him to murder Harry, he would spare her.
Xenophilius Lovegood betrays Harry in Harry Potter and the Deathly Hallows. The Death Eaters have Xenophilius' daughter, Luna.
Snape tells Voldemort that Harry Potter is to be moved from his place of safety on the next Saturday at nightfall.