The King's Queen (Nightmare Sans x Reader)

PLEASE READ BEFORE GETTING INTO THE STORY
Description: Your name is (Y/n) and you are originally from an au called Dreamtale! Your life hadn't been the easiest however, but you were quick to always move forward despite this... Before Nightmare had become corrupted, you were his best friend and lover. You kept him from his breaking point, you maintained his sanity and most importantly... returned his love. One thing that is definitely important about yourself is that you are a selective mute... And your only desired partner for conversation is the King of Negativity himself... But what will happen once the true evil lurking within your lover drowns out whatever light he had left? What will happen when you discover that the Nightmare you knew was replaced by a monster that still somehow holds love for you?
"And even with the evil finally in control of Nightmare, if both his sinister side and his old self agreed on something- then it would always be his priority... They both love her."

This is practically my first story that I have ever decided to share online. It is quite a terrifying experience for me, so I hope that anyone who decides to read this will enjoy it. Anyway, I should probably inform my readers about a few things. First off, my primary language is not English, however, I will still be making an effort with my grammar! Second off, I will try and update this as frequently as possible... Even though I can get somewhat shy or concerned about how my work goes. Otherwise, all you will need to know is this:
(Y/n): Your name
(F/n): Friend name
(E/c): Eye color
(H/l): Hair Length
(H/c): Hair color
(S/c): Skin color
(F/c): Favorite color
Some things I will likely determine for the reader, but what is posted above will be the basics. Please also note that this story may contain some content that would be best for more mature audiences.
Also, the cover image belongs to me, please do not use it without permission or steal it.