Things I Don't Know About You

"You will regret this."

Aspiring drama writer, Gam-Sa, breaks up with her long-term boyfriend, Ji-Ho, thinking he's been romantically involved with Eun-Gyeong. Despite Ji-Ho's ominous warning, Gam-Sa tries to carry on with her normal life...Until she hears Ji-Ho and Eun-Gyeong have been found dead together in a motel.

(Source: Manta, edited)