She liked him he loved another Like Heartstrings!

Dramas like heartstrings where the lead girl falls for the lead guy but he is in love with another girl but eventually he falls for her. The girl can be lead or secondary. 

Full House
Best Lover
Bring It On, Ghost
Cinderella and the Four Knights
Delightful Girl, Choon Hyang
Fated to Love You
Goodbye Mr. Black
Goong

Leh Ratree - Second lead fall in love with the (ex-)boyfriend of the female lead. (Love this two)
Gu Family Book - she is the only one who believes in him but he cannot get over his first love. She knows that but still wants to stay by his side

Do you also want recommendations where the female lead is in love with another person?

ok... Dramas the female character is in love with someone else:

Dream High - she is in love with one but another guy is always by her side, protect her and doesn't expect anything
Boys over Flowers - She is in love with the best friend of the guy who has a hit on her
Thumping Spike 2 -she is interested in a volleyball Player and a popular guy helps her do get his Attention... but step by step he starts to really like her
Best Time - she start to work in a company to get close to her high school crush and meet a guy who is interested in her and can simply read her mind
Jealousy Incarnate - she is obsessed with one guy but when she fall in love with his best friend (after he rejected her) he starts to become interested in her and fall in love... but will he fight for her and stab back his best friend?
When a Man loves - a man falls in love with a Girl he saved once but she is in love with his friend... or does she just use both of them?

Also wanna recommend:
Fight My Way
Scholar Who walks at night
lee soonshin is the best
rooftop prince
My GF is a gumiho
my Girl

Non-korean dramas:
Loving never forgetting
across the ocean to see you
Drunken to Love You
Sunny Happiness
H2
please love the useless me
kleun cheewit

More recommendations:

My lucky star
Nagareboshi
Wedding
Cain and Abel (kdrama)


Where the female lead loves someone else first:

That Fool
Pride
Weightlifting fairy Kim Bok Joo
Hotaru no Hikari
I'm Sorry, I Love You
It's Not That I Can't Marry, But I Don't Want To

Thanks @Izzydramalover

@Safae Thanks