It's Not Me, It's You by Alex Light

Jackie Myers is a fraud. Or she might be a genius—the jury’s still out. The thing is, she secretly runs "pleasebreakmyheart," a gone-viral account aimed at breaking hearts and ending relationships—and she just used it to break up her insufferable eternal nemesis's picture-perfect relationship.

Wilson is the buttoned-up, type-A assistant manager of her nightmares—but it turns out he’s also, apparently, a really great boyfriend.

So with her conscience (and paycheck) on the line, Jackie decides there’s only one thing to do: She’s going to help Wilson win his ex-girlfriend back. Which should be easy, considering Jackie hates him…right?