1-Title: "Breakup Chronicles" is an interesting title, it doesn't necessarily entail of any specific theme or genre, other than Romance and perhaps Drama. It's a bit confusing though, it may mislead some readers into thinking that the story consists of nothing but separate, unrelated chapters, each containing different plot/setting/characters. At least that's the message I've received.
2-Description/Foreword: Right, I can see you've got an idea of the theme and it's pretty clear (It's a back and forth between Romance and Drama). The description doesn't investigate into the title nor does it add something new, we've realised that there are two main characters (from the poster) and the description merely rephrases the title in a more detailed way. I think you should supply the readers with a more insightful glimpse into the general plot without giving too much, it doesn't have to be generous or lengthy, just sufficiently done. Also, the poster is really beautiful and fits the overall theme of the layout and colour palette.
3-Plot: The beginning is very interesting, we're immediately introduced to the main character (or one of the two main characters) Chaeyoung, and you've used the third-person narrative voice which is usually recommended in dramatic stories.
Now let's talk about the diction in your story, there are three necessary elements regarding diction that must be used in every story: Speech effectiveness, speech clearness, and speech correctness. The speech effectiveness in your story is rather weak, sufficient, but weak. Here's the issue, your story revolves around romance and drama, sometimes even tragedy, and this means that your choice of words needs to be stronger in order to obtain a reactive feedback. Try to use more sensitive synonyms and try to employ them as a connective agent between your message and the audience's hearts.
Speech clearness is so far, valid and intuitive, you've refrained from using unpopular terms and foreign language, which is usually used in drama but when you infuse that with post-modernist settings, it tends to grow more complicated. But you needn't worry about that.
Regarding the speech correctness, there are countless grammatical issues within the first and second chapters alone. English might not be your native language but your story shouldn't suffer because of such issue; consider running it through a Beta reader first. Let's investigate more deeply into the issue, your choice of words is not by any means bad, it's well but it's incorrect in regards to the sentence structure. Let me provide an example, during chapter no.2, in the first paragraph, “The students in the canteen made Chaeyoung and Lisa to groan." The additional preposition "to" is unnecessary in this case, you could say "The students in the canteen pushed Chaeyoung and Lisa to groan". The syntactic issues in your story doesn't render the reader incapable of grasping the core meaning of your plot, but it does pushes them to become slight