Romeo and Juliet/ Enemies to lovers

Close to what you are looking for

• Empress Ki (2013) - I don't want to say too much because I loved not knowing anything about this drama before watching it! Impossible love! They love each other but people are trying to keep them apart. I really think this could be what you're looking for! It's complicated to explain without spoiling you, so I'll not explaining further unless you ask me expressly! I really think it meets your requirements! Tragic ending with the romance! 
• Pinocchio (2014) - The love that the two main leads share is full of pitfalls, especially due to the past of the Main Lead. Their love is impossible because of their respective family situation (He is her "adoptive" uncle, the main lead was adopted by the female lead's grandfather when he was a child, they are not related by blood at all! But they are part of the same family in a way. Moreover, the Main Lead is looking to revenge his father which will directly affect the Female Lead... No Enemies to Lovers! Happy Ending for the main couple
• Come and Hug Me (2018) - When they were kids, Male Lead's father killed Female Lead's parents while they were in love. Years later, they meet again... An impossible love because of their past... Questions around the guilt, the consequences of the past on the present, etc... I think this is exactly what you are looking for! Happy Ending

Dramas that you might like but that don't really fill all your requirements (More or less matches the vibe I think you are looking for)

• Beautiful Secret (2015) -  It's a complicated family story on the female lead's side mainly (main plot with the romance).  It seems to me that at the beginning her relationship with the main lead is what we call "Enemies to Lovers". Many obstacles will be put in their way because of their respective families.  The main couple ends up together, so there is a happy ending!
• Devil Beside You (2005) - One of my favorite Enemies to Lovers. The "Romeo and Juliet" aspect could come from their impossible love as they become siblings after the marriage of their parents! (This is not a spoiler, it's in the synopsis). I don't remember the atmosphere being "very heavy" if that's what you're looking for! But we have Enemies to Lovers and "An Impossible Love" (they mostly hide their relationship rather than avoid it...) They end up together, happy ending!
• The Smile Has Left Your Eyes (2018) -  The problem is not the family. Quite different from the story of Romeo and Juliet but I think their relationship can be similar. Tragic Ending

I wish at least one of my recs can reach your expectations or give you some ideas! 

 Valentina:

shows that are similar to Romeo and Juliet's storyline

• The Princess Wei Young - ML's family is responsible for the annihilation of the FL's family and kingdom. The ending is not completely tragic but definitely bittersweet. The ML dies several years after marrying the FL because of something he did to protect her. 
• Crash Landing on You - FL is South Korean. ML is a captain in the North Korean army.
• Love in the Moonlight - The ML is crown prince. The FL is a female circus performer living as a man and also the daughter of a former rebel leader (now in hiding) who tried to overthrow the ML's father / end the monarchy.
• Lost Love in Times - The ML is a prince. The FL is a sorceress. The royal family is forbidden from having relations with sorcerers, and the ML and FL are part of a prophecy fortelling that if they get together, calamity will follow.
• Mr. Sunshine - The ML was born into slavery, becomes an orphan and flees to America. He returns to Korea as the U.S. Acting Consul. The FL is the daughter of a rich and powerful aristocratic family and also secretly a rebel fighting against foreign control at a time when Japan, China, Russia and the US were all trying to assert their power. The ML and several other characters die tragically for love / fighting for Korean independence.
• The Princess's Man - The FL is the daughter of a powerful political figure (prime minister or something like that). The ML is a young and talented scholar who gets caught up in political events. I don't remember the exact details, but I think the FL's father staged a coup? Whatever happened, the FL's father viewed the ML as a threat and had him exiled and then tried to have him killed. The ML returns as a rebel bent on getting revenge against the FL's father.
•  The Tale of Nokdu - The FL's family was killed by the King. The ML doesn't know it, but he's the King's son.
• The Masked Lover - The ML is a police officer who goes on an unofficial / personal undercover mission to expose the crimes of a female mafia boss responsible for harming his friend. The FL is an architect and daughter of a mafia family. Her twin is a mafia boss. 

 Cate:

The Hymn of Death - This story is just like Romeo and Juliet

+1 one of exact recommendation

Girls' Generation 1979  I've just finished it and was great drama, there are 2 female leads and one of them has very Romeo/Juliet like love happy end

A Love To Kill revenge and hate to love, very emotional story but it will make you cry, not happy end, though until the end it is already paintful love but also great epic and very very emotional

Kill It contract killer and detective not happy end

p.s

My Country: The New Age it is more Romeo and Romeo ))) but I can't help it and I remember this drama, it's not gay theme, it's bromance, but it is so great so emotional, not many great romances would compare to the emotions it will make you feel, there is good romance too, but these 2 guys had friendship better then love, they cared each other more then loved ones. life makes childhood friends enemies, at list they stand on opposite sides, but... :))))