Harry Potter and the half blood prince

Ok so Harry told Professer Dumbledoe that he failed to get that lost memory from Professer Slughorn. Dumbledore looked quite surprised that Harry didn't do what he had asked. But again, the went into the Pensieve to see more of Tom Riddles life. A.K.A Voldermort. What Harry knows so far is that Voldemort killed khis muggle father and grandparents, killed a lady who had slytheirns locket [ which had belonged to his mother.] and a cup from Helga Hufflepuff. It seem ed that Voldemort had a crazy obsession with Hogwarts. Because when he became 18 he asked Professe Dippet- current headmaster at Hogwarts.- to teach. Dippet said no because he thought that ahe needed more expericne in the world of magic. Then, a few years later, Voldemort returned when Dumbledor became headmaster. Dumbledore refused and Voldemort was furious. Now, no one who has applied for the Defense agasint the dark arts job has never kept it. Starting at Quarrel who died then, Lupin, Moody, and now Snape. Who I fear will have much worse fate than all the rest. Harry has also sent his new house elf Kreacher and Dobby to spy on Malfoy. Tjae both tell Harry Draco is not doing anything that they can see.