TITLE
       The title itself is confusing to a reader. I know you were going for a tie in with "Stockholm Syndrome" but with the preposition "in" it makes it seem like it's based in the Swedish capital. Even if one doesn't try to take it literally, it doesn't really fit well with the fic as a whole. You wrote a rather disturbing story and it doesn't correlate with the title at all, the title by itself gives off a completely different feel that the fic overall. I would consider changing it to something more appropriate that would fit your story. Whenever you choose a title, always think about the reader. This is someone that has no idea what your story is going to be about, their first impression is the title then the summary.

SPELLING & GRAMMAR
      I would consider a beta reader because even with just looking at minor issues there is a good amount of them. There are misspellings, words that need a hyphen and many misuses of the comma in a sentence. Going in depth with grammar, there is a problem with using passive voice. Active voice makes it clear who is doing what. In an active sentence, the person that is acting is the subject. Passive sentences obscure or omit the sentence subject. An example of this: "His body is ravaged, but he's still alive." simply change it to "his body's ravaged" Another example: "and he soars so quickly his heart is lodged in his throat" simply change it to "gets lodged in his throat" Use passive voice when the sentence object is more important than the subject. Active voice is generally easier to read. Your use of transitional phrases is above average, good job with that! You also have a good vocabulary, great usage of sophisticated words, but there were some over-used words and phrases. I would get a thesaurus to reduce the usage of some of them (examples: really, thing, know, was and etc).
 

CHARACTERIZATION
    I will go more in depth with how rushed this is in the both and flow but because of that I found it very hard to sympathize with Beakhyun. His life is miserable and instead of going into detail to actually help people feel for him, every bad thing that happened to him was just listed in a paragraph. It was off putting. Also, Baekhyun would "rather be dead, but he doesn't throw himself out the window," I feel like this is a huge contradiction and the excuse that is given is a little weak. What gives Beakhyun motivation to keep on going through all of the hardship? As for Chanyeol, I liked the fact that he seemed sane and gentlemanly at first. But the drastic change in his personality wasn't very believable. Some hints about his alternate personality would have been interesting. Maybe a reason behind it? Multiple-personalities? There wasn't enough description on Chanyeol, his reasons or how he ticks.

PLOT
        The plot. You mentioned the ending was rushed but the story overall is very rushed. I feel like you would be able to create a better ending if you spent more time on the body of the fic. Everything in the fic happens rather quickly, nothing goes too in depth. While you have good descriptions of how Beakhyun is feeling, it's mainly skin deep. There isn't conflict and I don't feel like there is a . The beginning was rushed and lacked detail, the middle should have more depth since this is the part where feelings for Chanyeol start to brew. Despite it being rushed, you did a very good job of making it disturbing. The detail on how Chanyeol treats Baekhyun at the end is fantastic, gets the point across amazingly. This fic starts too quick, has great detail towards the end, then crashes into the end. Spend more time on the beginning, about Beakhyun's life, show how he is gravitated towards Chanyeol at first and how he slowly falls for him even with how it is treated terribly. The ending itself isn't bad, it's actually very good, it's just the transition to it is abrupt.

FLOW
     While reading this, I felt like this shouldn't be a one-shot, unless it was a very long one-shot. It was extremely rushed, this was covered in characterization and plot so I won't reiterate.
 

WRITING STYLE
    Your average sentence length is a little bit short. I would look through, or consult with a beta reader, to improve your sentences to make more complex sentences in your writing. Also, work on some of the simple starts of your sentences. A lot of the sentences start with "he" or a name or "It". Try to creatively arrange your sentence beginnings to break up the monotony and choppy style. Overall, the style was easy to understand and used a lot of description. Though the writing was a bit rushed at times. I really enjoyed the parts that were centered and italicized. I thought that was a really creative addition to the story.
 

OVERALL ENJOYMENT
    I enjoyed the vocabulary and descriptions of the fic but it wasn't my cup of tea. It was also rather rushed and if it was more fleshed out, more detail on the characters with their backgrounds it could definitely get a lot better.