The FL is caught between them. She has feelings for both of them and is conflicted, then she chooses the ML and ends up with him.
Would prefer if not a historical, but will take those as well.
Happy endings please.
Boys Over Flowers is currently the only one I can think that isn't historical.
For historical I'm pretty sure these fit those categories from what I can remember:
If I find anymore non historical ones I'll be sure to post them here for you since most of the ones I found are historical.
I just dropped it, so I don't know how it ends, but Cambrian Period fits all of your other criteria: action, romance, ML and SML are rivals on opposing sides + love rivals, FL has feelings for both of them, and it's not historical.
https://kisskh.at/19968-karn-la-krang-neungnai-hua-jai
https://kisskh.at/3623-sound-of-the-desert this is historical but she's torn a lot between the two
https://kisskh.at/4738-too-late-to-say-i-love-you she meets 3 guys in her life
https://kisskh.at/15999-moon-lovers-scarlet-heart-ryeo historical/time travel
