what you described is more in Japanese dramas, recomendations are all japanese too, so I'll try recommend something else, maybe not so much dark ones but still tabo/dark
When I Was the Most Beautiful brothers love same woman, this is great drama, very high quality, complex relationships and characters, firework of raw emotions, not pulled, even plot of first 6-7 episodes would be enough for complite drama, but it continues and every episode is interesting and new
A Love To Kil also brothers and 1 woman, ML tries to revenge on FL, emotional and kind of dark, paintful romance, but one of the memorable and emotional romance
Sealed with a Kiss Stockholm syndrom type love, obsessive ML
Hyena not dark but very unusual/taboo love/relationship, If I'll say why it would be spoiler. there are few leads, friends, but I only watched Shin Sung roks story line (plus this actor is soo sexy, though here he is very young and not villain type as his later roles)
Mr. Queen very funny and high quality drama, Taboo
Nine: Nine Times Time Travel not dark but there is taboo, which is spoiler ))
Anti hero SML/villain and FL:
A Man's Story
Lucifer