WWDD: S1E12 “PROPHECY GIRL”
Since finding the diary, Dawn's hardly had any time to find what she's looking for in Buffy's diary—monsters! vampires! magic! But Buffy's pre-1997 entries were mostly about shopping, her boyfriend (Jeffrey), and Christian Slater.
The next night, Buffy is out, again (probably with her vampire boyfriend!), while Dawn is at a group sleepover with the friends she made during her first year of school-Shannon, Melinda, and Janice. They talk about boys (have you seen the boy from P.E.?!), school, and siblings. Dawn tells her friends about her sister kissing a boy and Shannon discloses that her older brother knows a girl who died ‘cause she choked on her boyfriend’s tongue. Their giggling is interrupted by shaking ground beneath them--an earthquake (a 5.1, at least).
Buffy comes home from school the next day upset and looks through old photo albums to the sound of melancholic ballads. When Dawn tries to ask what’s wrong, Buffy deflects, suddenly energized with the idea that they should all go away for the weekend. But Dawn has another sleepover planned with her friends (which is why Buffy suggests to Joyce they go out of town--just the two of them). Buffy deflates and returns to the photo album while Dawn passes her mom on her way out.
The following night, Buffy shows off her new dress in Dawn’s room, which Dawn loves. She asks Buffy if she’s going to the dance with the boy she was kissing and Buffy coyly remarks, “no,” before sharply adding Dawn cannot tell mom. Before she embarks to fight the Master, Buffy hugs Dawn tightly and tells her that she loves her and she'll be okay. Hours later, Buffy arrives home victorious and dirty. Dreaming of nothing but collapsing into her bed, Buffy’s caught off guard by what awaits her in her bedroom. Dawn sits on Buffy’s bed, diary open in her lap. Before Buffy can threaten her little sister with bodily injury, they lock eyes and Dawn declares, “I am so telling mom.