Can you recommend a really sad sad k-drama that makes your tears never end? It can be romantic, tragedy, violence, sickness. But personal i like tragedy best. 

I have seen A Werewolf Boy & Miracle in Cell No. 7.  And also 1 Litre of Tears. 

Thanks. :) 

Movies:
A Moment to Remember ---   My first K-movie, cried my heart out!
More Than Blue (aka A Story Sadder Than Sadness) --- Title says it all!

Drama:
East of Eden --- a non-typical melodrama. full of wonderful characters, intriguing plot ... lots of tears and lots of fun .... Romance, family, gangs, revenge and a wonderful hero!
Missing you.  too much crying
Loving You A Thousand Times
Harmony
As One
Maundy Thursday
A Moment to Remember
Classic
Windstruck
Cyborg She
Temptation of Wolves
More than Blue
i Give My First Love To You
Hello Brother
Koizora
BABO: Miracle of Giving Fool

49 Days
A Love to Kill
Im Sorry, I Love You
Q10
Zettai Kareshi
Thank you for the tips! 
Autumn Tale
Tree of Heaven
Uncontrollably Fond
Marriage Contract :(
That Winter ,The Wind Blows
Missing You
I second Marriage Contract. Every episode had me crying. 
Iljimae, Doctor Stranger had me crying but in 1st to 3rd episode.(I guess..) .  and some episode makes my tears burst  the next is exciting and thrill. .
You can try;
Gu Family Book, Hyde, Jekyll, Me (I cried in 19-20 episodes), Hwang Jin Yi, Warrior Baek Dong Soo, Blade Man
The Princess' Man, Joseon Gunman.King of Baking; Kim Tak Goo
Some of this dramas that I mention might not make you cry ( so sorry in advance,coz I cry easily) but they're good to watch.
(sorry for the wrong grammar... =D )
kill me heal me 
secret (2013)

secret is a lot more tragic and sad because of injustice and society
kill me heal me is sad because the male lead has multiple personalities which he can't control, it makes for a good laugh but still the sad scenes were sad