Get Even by Jade Church (Sun City book #1)

"I promised you'd scream and I like to keep my promises."

Don’t get mad, get even is advice Jamie Silver takes to heart when she discovers her boyfriend is sleeping with her best friend. What she doesn’t bank on is her hateful professor placing her on academic probation and it’s all her ex’s fault.

When his rival, Ryan Sommers, offers her a way to get back into her professor’s good books as well as get back at her ex, what’s a girl to do? Revenge is a dish best served hot.

Get Even is the first book in an interconnected series of standalones

Tropes you'll find:

morally grey FMC 
fake dating
Revenge 
College Romance