ML = Male Lead
SML = Second Male Lead
FL = Female Lead
SFL = Second Female Lead
Lost Romance (TW): The FL is sucked into a novel and is the villainess/SFL. She tries to seduce the ML but he likes the Main Girl of the novel. She gets hurt over and over again as sthe ML and Main Girl grow closer. FL gets closer the SFL and finally ML notices her.
Playful Kiss (SK): The FL likes the ML and he rejects her but she keeps on going after her. After she simply gives up, he shows interest before pushing her away again. He's also the son of a really rich CEO and starts to date the daughter of a potential investor.
My Husband in Law (THAI): The FL loves the ML and they're put into an arranged marriage. But he doesn't like her and only married her because he wanted to get rid of an annoying ex. He isn't in love with the ex anymore so that doesn't tick off "guy loves someone else", he just doesn't love ANYONE. But the reason he married her is cuz he used to love someone... Hope that makes sense.
Princess Hours (SK): The FL has a crush on the ML, and accidently sees him proposing to his girlfriend, he is rejected. ML catches her peeping and both are surprised when their parents arrange a marriage between the two days later. ML treats her like trash and tries to get back together with his girlfriend, but then the SML appears and ML starts to be nicer and dumps his girlfriend.
After the above titles. These stray a bit away from what you wanted, but they give off the same vibe so i figured why not...
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Theory of Love (THAI BL)): The ML1 finds out the ML2 is in love with him, breaks his heart, then regrets it after he realizes how much ML2 means to him.
Extraordinary You (SK): The FL likes the SML but he rejects her and regrets it after the ML appears.
Surplus Princess (SK): FL is a mermaid who falls in love with ML. He doesn't know who she is and ignores her. But once he gets to know her (and falls in love with her), she's already with the SML.
Find Yourself (C): The FL rejects the ML, they both start dating other people but can't forget each other.
The Liar and His Lover (SK): The ML uses the FL to write a piece of music then tells her to leave him alone. She joins his music company (it's a kpop thing) and the SML starts showing interest in her. The ML regrets throwing the FL aside for his music career.
The Last Empress (SK): The ML (honestly, this drama was a mess, can't tell who the actual ML was. For the sake of this thread, think of the emperor as the ML) rejects the FL, destroys her life etc. At the very end he realizes that he's in love with her.
Go Back Couple (SK): The ML and FL break up but he realizes he still loves her after the SML shows interest in her.