2. 'Innocence' (Season 2, Episode 14)
Buffy loses her virginity to her vampire boyfriend Angel, only to find he' s a different person the next morning – literally. He'd fallen in love with the slayer because he was cursed with a soul by a family of gypsies seeking vengeance. The catch: Once he finds true happiness, his soul will disappear. It's not only a metaphor for the worst of teenage sexual experiences, it also sets up several seasons of romantic angst and longing for Angel and Buffy – the perfect depiction of how first real love often feels. This plotline also hints for the first time at how ruthless Buffy would be in seeking emotional truth. There would be no perfect, quick magical fixes for the spell-crossed lovers.