Ouh sorry I was almost done with the list when I noticed you want a kdrama. Well I'm not erasing all I've written haha. So, there you have it a list that will not serve you haha.
The Wife's Secret was the one that came to mind at first but it is very long, so that's that.
Too late to say I love you, also long!
Summer's desire (2010 version is best)
Queen of Reversals (this is a very good match) Kdrama
Namtan Mai (also matches pretty well to your description)
I have a lover (look this one is super long but very well worth it, believe me)
Mia 2018 (The journey of a woman after a betrayal)
Last Friends to some degree but really this is much more than a break up story. Very heavy themes.
Fated to love you K drama
The spies who loved me kdrama