I am looking for dramas where the ML and FL are dating and the ML just disappear without explanation and come back after years (maybe with some company of a girl) while the FL just couldn't forget about him

It's historical but kind of fits - Gunman in Joseon. The leads were a couple, ML is presumed dead and appears years later with no explanation and a false identity and sort of involved with another girl (one sided). FL has never forgotten him.

fits all criterias:

Stairway to Heaven

Winter Sonata (but fl is about to wed, it's cancelled though)


not fits leaving for years but still leaving quite some times but fit the others:

Save The Last Dance For Me

Boys over Flowers


not fit dating but fit the others:

Autumn Tale