The Hatesick Diaries by Saffron A. Kent

Echo Adler hates Reign Davidson. He’s the reason the love of her life left her all alone and broken hearted two years ago.
So it should be easy to stay away.
It should be easy to not dream about his dark and mean eyes, or his cruel but sexy smirks. It should be easy to not think about the guy who ruined her happily ever after.
Only it’s not.
Sometimes his intense stares make her heart race, and those smirks of his make her breathless.
But it needs to stop.
Because she has a mission: to get back together with her ex-boyfriend. And Echo will be damned if she keeps dreaming about Reign.
The guy who not only makes her sick with hate but who also happens to be her ex’s best friend.