Sud Sai Pan

The Backstory: Mistaken Identity M.L. Thiti Suriyakan is a noble descendant who celebrates his graduation at a beach in Prachuap Khiri Khan. There, he meets Kandamanee, a woman who claims to be named Kandawasi Kirinesuan. Unbeknownst to Thiti, Kandamanee is actually Kandawasi’s twin sister. Thiti falls deeply in love with her, promising he will never marry anyone unless her name is "Kandawasi Kirinesuan." However, for Kandamanee, the affair is just a game. When Thiti asks her to wait while he builds his fortune, she disappears without a trace to pursue other men and a hedonistic lifestyle.
The Conflict: The Real Sister Years later, Thiti—who has now inherited a massive fortune from his grandfather—encounters the real Kandawasi at a party. He is overjoyed but confused when she claims not to know him. When he tries to remind her of their past, she slaps him, insulted. Thiti believes she is rejecting him because she thinks he is poor (not knowing about his inheritance). His mother, Pudtan, comforts him, saying it is better he learned her true nature before she knew of his wealth.
The Revenge Plot While Kandamanee continues to use her sister's name to trick men (including a playboy named Wasan who eventually dumps her), the real Kandawasi faces hardship at home due to her cruel stepmother, Urai. Kandawasi gets a job at Thiti's company. Thiti, still believing she is the woman who broke his heart, uses his position to exact revenge on her. Matters worsen when Wasan (now an accountant at the company) claims he also had a deep relationship with "Kandawasi," further convincing Thiti that she is a promiscuous woman who treats love as a game. Thiti decides to make Kandawasi fall in love with him just to hurt her. However, as Kandawasi struggles with family debts caused by her stepmother's gambling, she asks Thiti for help. He agrees on one condition: she must marry him without a legal registration. She accepts to save her family's honor.
The Twist: The Twin Returns Life in Thiti's house is a "cold war," and Kandawasi is treated poorly. Meanwhile, Kandamanee sees news of the wedding and realizes Thiti is now a billionaire. Driven by greed and jealousy, she seeks out Thiti, lying that she has always kept her promise to him. Thiti is moved by her "loyalty" and hates Kandawasi even more for "deceiving" him.
The Climax Thiti introduces Kandamanee to Kandawasi. Kandawasi is shocked to learn she has a twin sister. Kandamanee pretends to be sweet in front of Thiti but viciously attacks her sister in private, demanding Thiti back. Kandawasi decides to flee, confirming Thiti's belief that she never loved him. However, once Kandamanee moves in and impersonates Kandawasi, Thiti begins to feel something is wrong. He realizes his heart has actually bonded with the real Kandawasi, not the woman from his past.