I am just going to suggest I Need Romance because I don't see it anywhere on your list and it may or may not fit your criteria ( that would be a spoiler)...but I strongly suggest it :)
In Worlds Within (or The World That They Live In) the leads are ex-boyfriend and ex-girlfriend so the plot is pretty different, it fits your description :)
Sleepninja wrote: There is an area where people can ask for recommendations. You can browse there and see what people have posted. This should probably be moved to that section as well. :) Recommendation Forum < clicky
It's a good mystery story, plus has a great triangle (yeah, I know, but it's a Kdrama. lol) Guy/girl are friends, and guy begins to feel more for girl than friendship. Complicated by second guy who is likeable, who also becomes friends with the girl.
