can someone explain to me why they don’t end up together ? :((((

It's supposed to be a very realistic manhwa. Author-nim wanted to portray that if you're not meant to be then you're not meant to be despite of the efforts of trying to make the relationship work out. Plus, Nari and Mooki have very different personalities and views about love and relationship which probably one of the reasons why they didn't work out

ahhh i see :((( thank you for replying!!