During Harry Potter and the Deathly Hallows, Snape uses his Patronus to lead Harry to the sword of Gryffindor. ... After Voldemort killed her, Snape secretly changed sides and agreed to help Dumbledore protect Harry from Voldemort. With all of this, it seems that the answer is clear: Snape is a good person.

Did Snape really betray Dumbledore?

In return, Snape secretly allied himself with Dumbledore and the Order of the Phoenix as a double agent against Voldemort, using his powers of Occlumency to hide his betrayal from Voldemort. ... Even with his efforts to protect her, Snape felt responsible for Lily's death at Voldemort's hands.

Why did Snape turn bad?

Harry later discovered that Snape was once a Death Eater but had been vouched for by Dumbledore. Dumbledore told the Wizengamot that although Snape had indeed worked for Voldemort, he changed sides and turned spy against him. ... Karkaroff, who dreaded retribution from Voldemort, panicked and confided his fears in Snape.