Heys Guys, I need your help and even if Mydramalist is hella good, I cant seem to find any of the dramas I'm searching. I dont care which country its from, I just need it complete and subbed :p Okay, so right now, Im in revenge dramas or dark obscessive dramas with a sexy dark Male Lead :3 I've already seen Bad Guy, Shark, Innocent Man, My Princess Man, One Million Stars Falling from the Sky (which was hella good just saying), Taiyou no Kisetsu, Ouroboros... 

I mean, it cant be all right? I'm going through a tough time and right now, those kind of dramas are really helping! If you have any suggestions, well I'm all ears :) You've had my back and I've had yours, lets continue helping each other!!! Hehe thanks guys!!!

Bridal Mask sounds like just the thing you are looking for!
Other revenge dramas (I'll leave the judgement of sexy and dark up to you) and some other ideas:
The Devil (didn't finish it, but I will someday!  I can say it was good for the first 11 eps, at least)
Equator Man (kinda addictive in parts, but the writing of the female lead is meh in the later eps.  Still a pretty fun drama)
Bridal Mask (my favorite drama, period)
Chuno (not really revenge, but might be close)
Warrior Baek Dong Soo?  I really hesitate to recommend it because for me it sure went straight to hell somewhere in the middle and never came back (lol), but you might like it.
Hehehhe I've seen Bridal Mask :) That drama hurted me, the way the friendship between the two men went south... I was shouting and screaming, being all like, You were best friends, you two were so pure together! Whhyyyyyyy?!!!! Halala, good times :)
Chuno? Never heard of it, I'll see thanks! Equator Man too :) For the others, I've seen them too XD For the Devil, I assume you saw the korean version? I saw both the japanese and korean version XD You should continue it! It gets darker and darker :o
These are some I watched that are on the darker side and/or contain a revenge plot:

City Hunter
Ghost
Iljimae
My Beautiful Bride
Secret
That Winter, The Wind Blows
Time Between Dog and Wolf

They might not be exact matches, but they're worth a try. ^^
The Incarnation of Money
Beyond the Clouds
Nirvana in Fire
Last
Joseon Gunman
I'm Sorry, I Love You
Goodbye Mr. Black
Thank You Guys :) You're all sweethearts, bless your souls! See you in kdramaland XD
No one has mentioned Remember – War of the Son yet, it's quite depressing though. :( I enjoyed Warrior Baek Dong Soo too but the dark male lead was rather sweet than sexy.

I forgot Liar Game!!! Cunning, shady, super sexy and handsome Shin Sung Rok was amazing in that one.
East of Eden --- The ultimate revenge action romance melodrama! .... The hero is not dark, but the entire family is driven by revenge, plenty of dark sexy characters ..... two babies switched at birth by a vindictive nurse, so each is being raised by his family's enemy ..... many perspectives on various aspects and types of revenge .... well developed characters.
Hero is selfless, driven, romantic .... a genuine good-guy, wrapped in a bad-boy image.
Revenge:

Cain and abel
Good bye Mr. Black
I'm sorry I love you
Innocent Man
Maou
Ryusei no kizuna


Dark:
Byakuyakou
Que sera sera
Maybe byakouyakou fits in that category? 
the others I think of have already been cited but if I remember another I'll comment again ~ I know there are some more since I love this genre too hehe 
maybe heartless city too?