Since there are so many j dorama pros here, was wondering if anyone knows this series? I forgot the title and need some help. If anyone knows please tell me

Its about this young guy, he's been chasing this girl all the way from high school until now until he meets another girl. They bumped into each other at the airport and mistakenly exchanged passports. They somehow get together, and somehow the girl gets pregnant, and then the guy goes for national service, comes back as a pilot, but along the way screws up his relationship with his her. They both didn't marry each other yet altho they have a daughter.

First epi goes something like this.

The lead actor arrives at the airport (came back from somewhere) and then tries to sneak into the girl's (he's been chasing since highschool) apartment to surprise her for her bday. But shes not interested in him at all and goes out with another damn hot guy.

Dont know perhaps this is a korean series =/ but i'm pretty sure its japanese.