Love's Better Than Immortality (2019) - This fulfills your requirements! 100% :) 

Awesome drama and unforgettable romance ("Villain" chases the FL and Obsessive ML)

I don't know if this fits all that well but you could try..

Bloody Romance It's kind of dark.. I think the name says all. I did end up dropping it before I got to the ending so I don't know how it ends but you could give it a shot. 

Secret 

That Winter the Wind Blows

Flower of Evil 

Kill It (only hinted romance)

One Million Stars Falling from the Sky

Mitsu no Aji 

Majo no Jouken 

 Dramalover203:

Secret 

That Winter the Wind Blows

Flower of Evil 

Kill It (only hinted romance)

One Million Stars Falling from the Sky

Mitsu no Aji 

Majo no Jouken 

Thank you! 

 LoveYouDramaWorld:

Love's Better Than Immortality (2019) - This fulfills your requirements! 100% :) 

Awesome drama and unforgettable romance ("Villain" chases the FL and Obsessive ML)

I did start this but it felt like a typical historical romance so i dropped it :( but I'll definitely check this out again thank you! 

I am awed that there is no Innocent Man (2012), I would also recommend Hotel King (2014) (makjang dark feels), and Before We get married Puff Kuo and Jasper Liu

 Take me away:
I'll definitely check this out again

I'm sure you will dropp it again, I can't understand why it's popular or how it is dark or ML is dark... it's very cheep primitive cliche drama with bed production quality and I couldn't take ML seriously especially as dark-kinda bad guy...

try "love to kill" or "cruel city" (second one isn't romance centered but story, ML and romance, everything is kind of dark and mature, twists and turns in every episode. Name is very correct to the feeling of the drama - cruel city (also called heartless city), really great drama!

 Moonlight:

I am awed that there is no Innocent Man (2012), I would also recommend Hotel King (2014) (makjang dark feels), and Before We get married Puff Kuo and Jasper Liu

Thank you! 

 emaureeng:

Mask (2015) - has a heck of an opening episode which probably shouldn't be examined too closely. The MDL description says that the chaebol heir is "distrusting".  More like cuckoo for Cocoa Puffs - he's paranoid and sometimes hallucinates (there's a reason).  He's also the heroine's only hope and she, his. This one is over the top at times, but I greatly enjoyed it. Multiple villains.

Ohh i remember this!  Idk why i never continued it even though i enjoyed it thank you for reminding me of this! 

 Moonlight:
Before We get married Puff Kuo and Jasper Liu

That's not a dark romance at all though. More like a guy who has a gf he no longer loves chases after a girl who has a bf that no longer cares for her.

What's wrong with secretary Kim 

 foxyjo:

What's wrong with secretary Kim 

Really? When I was watching it, I didn't think it was that dark... Maybe I have a wrong memory about it but... yeah I think it's light and cute instead.