In addition:
Dream High (totally this plot)
heart to heart
lets eat 2
maids
i need romance 3
Discovery of Love and I need romance 2 (interestingly, this has the same female lead Jung yumi. In both dramas the guy was an ass, and they were ex-es, and she has a new BF)
falling for innocence (does it count if the guy she likes is dead)
49 days (though this ended very sad)
Big (in a very weird love triangle)
one of the the drama special that starred kara members, titled have coffee with and angel
feast of the gods (though i do think the guy that ended up with the female lead is actually the 2nd lead)
the story of the maknae and her senior from age of youth
The Story of yeonTae and sangmin from Five Children. They were the secondary characters though. But one of the best ever with this kind of scenario.