Lhong Ngao Jun (2006)

Pim's half-sister Khem goes out with guys pretending to be Pim. After getting dumped by Khem, one of the guys dies in a car crash. His friend Aae accuses 'Pim' of being the cause and vows to get revenge on her and gets engaged to Khem so he can get closer to Pim in order to make her life miserable. Pim on the other hand has no clue why she's being stalked/bullied by this psychopath.