ML and FL want to be together but can't

There's a lot of sexual tension between main characters, they enjoy spending time with each other, but for some reason they kind of don't allow themselves to kiss and be together and preferably the ending is sad and they don't end up together. But if they do get together in the end, the plot described above should be a significant part of the story...

the ML is preferably around 35-40+ years old, not too young

Any nationality is fine, if it's a film - even better, and not necessarily asian as long as the show's/film's rating is not too low, I watch dramas from all over the world

If you don't mind Old Hollywood Heaven Knows Mr. Allison fits perfectly (tons of sexual tension, they obviously love each other, but FL can't break her vows as a nun and ML has to return to the war)

Also:

• The Flowers of War 

And the characters are younger than 35, but otherwise these fit:

• Dear Mayang Street 
• Homme Fatale 
• The Chinese Widow
• The Curse of Turandot 
• Till We Meet Again on the Lily Hill