It’s Gone Girl by Gillian Flynn, can be found at any library- also was made into an award winning movie but the book is way better.
There used to be a link to the entire novel online but I can’t find it- nevertheless that’s the author
@AuthorMisty You're welcome! I've read almost all your books and so far, I love it! It's so hard to find a good Final Fantasy's fanfics (I love Vanitas, Zack and Prompto more than the others though). Anyway, I'll look forward for the sequel! (⌒▽⌒)