Sugarholic (2005)

Blurb:
As part of her grandmother’s scheme, twenty-year-old Jae-Gyu is sent from her secluded country village to the big city. Completely out of her element and out of money, Jae-Gyu manages to get into trouble as soon as she gets off the bus. She expected the move would be rough, but she never thought she’d meet the last person she ever wanted to see again — Hee-Do, a boy from grade school whom she bullied mercilessly. Even though he’s a big-time rock star now, he still remembers his childhood tormentor. Is he out for revenge? Or is it something quite different…?

Source: www.anisearch.com/manga/5984