It's a pretty good K-Drama and I'm very picky when it comes to watching K-Dramas, some people may have not to like the ending, but I thought I was pretty realistic.
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In the last episodes when she's breaking up with him because she wants him to do what he loves without any problems as well as her wanting to catch up on her dreams, sometimes the right person comes but not at the right time and this was clearly one of those, but at the end of the last ep, we can see them reconnecting in a better time when both of them have to reach their goals and are stable in both of their careers.