1) When he returns to Hogwarts for his 8th year, Harry discovers that Snape is hiding something. Harry's determined to help Snape, but Snape is reluctant to reveal the truth.
2) Harry discovers that a Slytherin 1st year student is being bullied. When he takes the student under his wing he finds himself becoming closer to Severus Snape.
3) Severus finds himself getting inappropriate hard-ons around Harry and decides he must have been cursed.