Buffy the Vampire Slayer 2x16

Bewitched, Bothered and Bewildered

Xander tries to use Valentines Day to further his relationship with Cordelia but she succumbs to peer pressure and breaks up with him. With the help of Amy (who is exploring her mother’s witch powers), he puts a love spell on her which goes horribly wrong, turning him into every woman’s desire; except Cordelia’s.