Bound to the Abyss (слэш)

[Harry had to understand in order to grasp Snape's dark kind of beauty.] Deeply disturbed, Harry witnesses the full extent of Snape's most terrible memory in the Pensieve. Horrified, he vows to distance himself as much as possible from his father—but, of course, he also needs to learn Occlumency to hide his snooping from Snape. Meanwhile, Severus is plagued by doubts—Potter is undeniably an unbearable nuisance, but can he, in good conscience, truly support Dumbledore's plan for the boy? (SS/HP, Snarry, AU from fifth year)