Everneath by Brodi Ashton

Last spring, Nikki Beckett vanished, sucked into an underworld known as the Everneath, where immortals Feed on the emotions of despairing humans. Now she's returned- to her old life, her family, her friends- before being banished back to the underworld... this time forever. 
She has six months before the Everneath comes to claim her, six months for good-byes she can't find the words for, six months to find redemption, if it exists. 

Nikki longs to spend these months reconnecting with her boyfriend, Jack, the one person she loves more than anything. But there's a problem: Cole, the smoldering immortal who first enticed her to the Everneath, has followed Nikki to the mortal world. And he'll do whatever it takes to bring her back- this time as his queen. 
As Nikki's time grows short and her relationships begin slipping from her grasp, she's forced to make the hardest decision of her life: find a way to cheat fate and remain on the Surface with Jack or return to the Everneath and become Cole's..
@Carti Alese