So ML liked FL who liked SML. He ended up with an unrequited love and she ended up dating SML but had a painful breakup and now years later they all meet again.

Have seen this plot plenty of times in many Chinese and Korean dramas before.
FL is still hurt over breakup, SML will try to get back with her, ML will try to be with her and help her get over SML. In the end ML/FL will end up together..........End of Story
No wonder this drama has only 8 eps and will be over in 4 weeks since there is nothing much to add to it. Other than 1 or 2 moments where things go different than expected, overall it is simply mid.

The only things saving this drama is the cute chemistry between leads otherwise it is generic.

( Kim So Hyun needs to choose better scripts and not the same cliche trope again and again)