Discovery of Romance (2014)

Same scriptwriter (she has typical own "handwriting") and you will find Sung Joon in both shows. DoR can be INR4.

Similar love triangle, where a woman can't decide between someone who seems perfect and someone who she used to love. I preferred Jealousy Incarnate but both are worth watching.

first thing which is similar is ex-lovers getting together trope and the other would be the interview thing anytime in the episode which not many K-dramas do
and yah both have Kim Seul Gi so that's a plus point from my side

Similar vibes on long-term dated exes who meet after years and work together at an architecture company.

The same concept: a long time couple broke up after some misunderstandings between them, but they met again after a while and the girl has a perfect boyfriend that will be marrying soon.

In both, ex returns and start their relationship over again and FL gets involved with someone else but ML wins her over.

In both, ex boyfriend returns in FL's life when she's in a relationship and they kind of end up cheating.

Que Sera Sera stars Eric and Jung Yu Mi, approximately 7 years ago, and is responsible for fans calling them the 'Elevator Couple'. It tells the story of a man who is experienced in getting what he wants from women, without loving any of them, and a woman who has never been kissed. As the drama progresses, the chemistry increases between the two, which results in some romantic and passionate scenes.

you will find similar atmosphere or feeling...
some characters are quite similar and so the story..
and also the craziness comedy <3 :DD
if you love this drama you will definitely love the other one :)