I want a drama or a movie were one of the lead is a foreigner, even if not the lead, he/she should be relevant to the story and should have romance with his/her character.

The only thing I can think of is Failan (South Korean movie with a Hong Konger female lead).

If you don't mind non-Korean movies/dramas, there's also Last Life in the Universe (Thai movie with a Japanese male lead) and Massan (Japanese drama with a American female lead; the actor is American, but I think her character was supposed to be Scottish)

My Brother's Husband but its only 3 episodes

Never Said Goodbye is a Taiwanese movie starring Zhou Dongyu (Chinese)  and Lee Joon Ki (Korean). It's a really nice movie, I recommend you to try it out if you're into romance and a little bit of comedy.

seducing mr. perfect. 

I mean Daniel Henney is korean but he's from America and he speaks like no word Korean in that movie.

 Chinese Hero Zhao Zi Long was a Chinese drama with two Korean leads, Im Yoona and Kang Junghoon. It has 60 episodes though that are all 40 minutes each.. 

The Lover, a Korean drama, had one of its (many) leads as Japanese member Terada Takuya of Cross Gene.  

I think that's all I've seen foreign lead wise... I know there was a couple Chinese movies with Korean idol members as leads I think but I can't remember the titles.