Promiscuous(2002)

Harenchi

"Maybe the reason why I'm drawn to you is love's gravitational force--?" Sonoko, who spends her uninspiring high school days just passing the time, kisses her friend's boyfriend after school in the science room b/c "one thing sort of led to another". However, Itou, the school's star student walks right in on them! She tries to run away by jumping out the window, but...?

This manga volume also includes two other cute one shots titled "Denpa" and "Cream Soda"