Any shows (mainly Japanese or Korean) where the second male lead becomes obsessed with the female lead and tries to steal her away from the male lead. Maybe the female lead liked him at first, but then she falls for the male lead and that sends the second male lead over the edge. He does everything in his power to break them up. Maybe he kisses her and the male lead catches them so the male lead thinks she's cheating or something. He's basically behind many misunderstandings for the couple. In the end, he gives up or dies. 

Like Sassy Girl Chun-hyang.

Missing you (at first she's living with the second male lead and when she starts falling for the ML, he won't let her go)

Que sera, sera (but it's even more twisted and complicated between the 2nd ML and the FL)

Loving, never forgetting (C-drama but has a heavy element of the 2nd ML doing everything to break up the main couple).


historical drama the The Princess' Man, 2nd male lead also falls in love with female lead and betrays male lead who was his best friend, while seeking out his own selfish ambitions. 2nd male lead's love is very one sided and unrequited for her even though she tells him she doesn't like him and will not marry him.  

  • The King's Woman* - two of the male leads arguably fit in different ways
  • General and I* (I haven't finished this one yet)
  • The Princess Wei Young*
  • The Imperial Doctress*
  • Snow Lotus - a very... unique take on the dynamic you described (involves reincarnation) 
  • Hi! School Love On - both the second male lead and third male lead sort of fit to a certain extent

I also think Princess Agents* is worth mentioning, even though the FL only realizes her feelings for the ML in the last moments of the drama, the second male lead doesn't give up or die, and there's a cliffhanger ending

*Chinese

Gaksital is literally that with the crazy second male lead

 Missing You's 2nd male lead matches a lot of your description.