Posted:
If by "some parts of the original story" you mean copying entire sentences and paragraphs from the original story like you did with the prologue, that's still plagiarism, even if you add your own words here and there. It's not fair for you to take any of the credit for someone else's work.
However, if you're inspired by the original *idea* of the story (in this case, fake boyfriend at exes wedding), I don't find anything wrong with writing a similar plot *as long as you use your own words*.
127