Transmigration: Cannon Fodder Can Surpass Female Lead

I remember I got stood up on our anniversary. I remember my boyfriend telling me he was busy to come and he was sorry that he couldn't. I remember going to our apartment to sleep. I remember the noise I heard, before entering our bedroom to see my best friend and boyfriend making out. I remembered how I screamed. But I SURE AS HELL DO NOT REMEMBER HOW I GOT HERE!
A certain System: "Hmm... Host will you please try to calm down"
Me: *Looks at system with murderous intentions.*
A certain System: I will explain everything.
All pictures or media used do not belong to me but to either google or Pinterest.
That is how my life went on after that night.

I hate spoilers so I will not describe the entire book to you. But this story is a transmigration story based on inspiration I got from reading Chinese novels. I am not Chinese, please do not try and guess my nationality. This is a 1 v 1 story.
Read to find out what the story is about. Unravel this mystery.
PS: This novel is not for kids or younger teens so don't criticize any graphic scene. Grammatical corrections and questions are always appreciated.