Beyond Evil? hahaha, kidding. (But also, kind of not kidding.)

Honestly the only one I can think of that I've watched might be Strangers Again. But to be honest, I liked this drama more for the discussions with fellow Beanies than for it's actual content. Hot takes galore.

The Third Charm -- I think it's too raw and real, I could never watch it again. And The World of the Married, blood-boilingly frustrating and agonizing!

The Third Charm is really good and realistic.

The Smile Has Left Your Eyes will make you suffer a lot.

Que Sera Sera has characters who don't really know what they really want.

Call It Love.
My Liberation Notes. This one has three.
Strangers Again. Oooooh. This one really stretched it to the limit.
Search WWW. (One of the leads' relationship, I think Jeon Hye-jin's)
The Third Charm.
Queen Seon-deok.
Gwangaetto, The Great Conqueror (Damdeok x his first crown princess consort).

I'm Sorry I Love You: the OTP has so little precious time together, yet so much of it is wasted due to misunderstanding and noble idiocy. Hurts so good though...

I dropped Youth of May around episode 2, but I know this drama has the elements you are looking for, writer-nim.

OTP not together in the end… painful…

To be honest, the first drama on top of my head is Oh! Master. But the pain you might feel watching it will most likely be due to the poor storyline/script/directing. It was so bad it was excruciating to watch.

Sorry, this comment does not count as rec, but more of a warning.

I’m sorry Lee Min-ki and Na-na. I love you but…

Just dropping by to thank everyone for your recommendations - they all will be noted to make sure I NEVER touch any of these shows)))

Twenty-Five Twenty-One maybe. There is a huge uproar over the ending but I love it. I personally think it is the right ending.

I just watched Twelve Nights and thought it was pretty brutal on the agonizingly frustrating meter . . .

HI, BYE MAMA. You cannot root against any of the main characters. The sliver of hope was never meant to be for the OTP. The show ended in a proper way.

- Mr. Sunshine

- Memories of the Alhambra (depending on your interpretation of the muddled ending)

What Happened In Bali.
Just warning, it is an old school k-melo... with a brutal ending.

Moon Lovers: Scarlet Heart Ryeo
Need I say more?

Not counting Call It Love, I realize it's been ages since I last enjoy romance in kdrama. The one that comes to my mind is Princess' Man. It's achingly beautiful. I grew attached to their forbidden love story. Call me weird but I kind of love their fierce love and their struggle and the heartbreak. It truly makes a precious love story.

Gangnam Scandal...123 episodes of what you're looking for :)

Tree of heaven

Empress Ki has 2 agonizing love stories for the price of one.

Seven Days Queen (Pure agony with a more bitter than sweet ending)

Not a kdrama but the Taiwanese drama Someday or One Day might also fit the criteria. It is my personal fav bittersweet love story. Also the Chinese movie Better Days (another favourite) and the Japanese drama Soredemo, Ikite Yuku would be my other recommendations.

Interest of Love. Such a frustrating ending (for me).

Immediately, I thought of I'm Sorry, I Love You with So Ji-sub and Im Soo-jung. The title just screams agonizing love story. If asked for a top ten list of agonizing love stories, I'd probably just pick ten episode from that drama.

Que Sera Sera, also already mentioned by others here, is a good one, though the ending is open to interpretation.

And then there's A Love to Kill with Rain and Shin Min-a, which I don't remember as being good, but it was agonizing, and there was a memorable kissing scene.

Finally, the movie More than Blue with Lee Bo-Young and Kwon Sang-woo.

No, nope, never again. So triggered by this thread. A simple word analysis comes up with every term associated with abusive relationships. This written by someone who sat in a parked car sobbing to Aretha Franklin's "Never Loved a Man".
Time to change the tune to I Will Survive.

I don't think anyone has mentioned The Hymn of Death yet.

I think the 2019 dramaPossessed will be right up your alley.

TITANIC 😉

Are we going for melo without a happy ending? Or just no happy ending in general?

It depends who you ship, but if you found yourself rooting for the ‘wrong’ guy I’d say both ANSWER ME 1994 & ANSWER 1988 would be a torturous experience. Particularly Jung-hwan’s ‘confession’ will KILL YOU. (Did not include ANSWER ME 1997 cause if you rooted for the teacher, I’m JUDGING you so hard right now)

DREAM HIGH S1
They worked so hard to be the best idols in the industry but at what cost? Love?

My LOVE FROM ANOTHER STAR & CRASH LANDING ON YOU
Both had bittersweet endings, one falls for an Alien who looks awfully like Kim Soo-hyun and the other falls for a North Korean solider who looks identical to Hyun-Bin

MY FIRST TIME
ML doesn’t get the ‘girl’. It’s about their friendship and his unrequited love.

ARCHITECTURE 101 (film)
Oh boy this didn’t age well. There are a LOT of famous actors in this and it fits your description but ummm with a big caveat, it features a lot of rapey dialogue…

SUNNY (film)
I wouldn’t say it was a torturous love, but it was the female lead’s first ‘unrequited’ love. Anyway the film is all about female friendships and one of my all time favourites

20th century girl has all that with a nostalgia element, in a bite sized format because it’s a film.

Just wanted to chime in that I did like most of the juicy angst in The Interest of Love too! Seems kinda uncommon. I can't think of anything similar that I've seen. ...maybe Flower of Evil? I loved the heightened emotions from the male lead. It is a mystery/crime drama btw.

This is an unorthodox suggestion BUT it's the drama I go to for guilty-pleasure pain lol. Tempted (or I think the alternative title is 'The Great Seducer) is painful for many reasons, but the love-line between the main couple is definitely one of those reasons. The ending implies a possible happy ending but it is kind of left open and honestly if anything, to me, it was just more painful because it didn't make sense (how was that meant to be a resolution to everything that happened??). It's kind of like a train-wreck you can't take your eyes off though, so it's nowhere near as poignant as Interest of Love but it does give you the same kind of feelings, if that makes sense?

Another two that technically fit the box is 25-21and Goblin. 25-21 is very sweetly agonising, especially in the second half. Might not be the exact same vibe as Interest of Love but it was just as bittersweet imo. And Goblin is basically a synonym for angst and ill fated romance in my dictionary 😂

Twenty Five Twenty One is the most frustrating ending you might watch. You know very well they couldn't be together, at least unless they do some character development first, but you cry your heart out on their separation scene.

For me, A Piece Of Your Mind (2020) still left me feeling sad and I consider this drama under rated. For some reason it was cut from the original 16 episodes to 12 episodes. Yet the story as it unfolds is very compelling drawing us deep into the memories of a woman after her death. The love, loss and the sadness of the protagonist for his first love. There is not much romance in this slow-paced drama but like an artist painting a picture, it slowly unravels itself to be a beautiful drawing.

Awaken (2020/2021)
Behind Every Star (2022)
Cheese in the Trap (2016)
Heartless City (2013)
Justice (2019)
Mouse (2021)
My Heart Twinkle Twinkle (2015)
Seasons of Blossom (2022)
Sponsor (2022)
Reunited Worlds (2017)
The Smile Has Left Your Eyes (2018)
Uncontrollably Fond (2016)
VIP (2019)

The top three shows that fit this description are
1. Twenty Five Twenty One
2. Twenty Five Twenty One
3. Twenty Five Twenty One

It's especially impactful because the writer/director/actors did an incredibly perfect job building up such a beautiful creation, and then it seems like they just wanted to see the world burn.

The relationship between the female lead and her rival was executed to perfection. The formation of that fab 5 friend groups was portrayed to perfection as well. The mother daughter relationship was so realistically portrayed where I had flashbacks of my actual relationship with my mother. The father daughter relationship touched my heart and was totally heartfelt and heartbreaking. The mother and coach relationship was realistic and reminded us all how friends can be lost. The story arch behind the FL and ML was.........aaaaaaaauuuggghhhhhhhhhhhhhhh! (going to my corner to cry).

The Red Sleeve?

Queen for Seven Days - this one is very heartwrenchingly good. Get boxes of tissues ready.

I'm Sorry, I Love You - this was so long ago but I remember it having a bittersweet ending.

Call It Love - slow burn but still great. I love the leads despite their situation.

Bulgasal. Agonizing yet perfect ending.

I scrolled down and I was surprised I didn't see 'Misty'. Could it have possibly gotten any more tragic?

Also 'Pretty Noona Who Buys Me Food'/'Something In The Rain'. How many years were they separated at the end? I didn't buy that tacked-on reunited scene, it felt like something the studio strong-armed them into patching on.

And a joke submission: 'Melting Me Softly'. Didn't they have to put the heroine back in the deef freeze for 20 years to keep her alive, or something like that.

Lovers in Paris! Hahaha

I used to live in the angst romance cave, but I’ve now taken up residence in the fluffy clouds of happily ever after. That being said, the drama that first came to my mind when I read this post was MIRROR OF THE WITCH: historical fantasy about a cursed princess and star-crossed lovers. It’s long at 20 episodes, and the ending will gut you. Bonus: this one also has Moon Ga Young, playing a lovelorn warrior.