The Darkest Captive by Gena Showalter

For centuries, Galen the Treacherous has been the most hated immortal in the Underworld. With good reason! This bad boy of bad boys has lied, stolen, cheated and killed with abandon. Possessed by the demons of Jealousy and False Hope, he has always lived for a single purpose: destroy everything.

Then he met her.
Former demon turned human femme fatale — Legion Honey — sought to kill Galen, but ended up parting with her virginity instead. Afraid of their sizzling connection, she ran away…and ended up trapped in hell, tortured and abused in the worst of ways. Now she’s free, and a shell of herself, afraid of her own shadow.

Galen’s hunger for Legion has only grown. Now the warrior with nothing to lose must help her rekindle the fire that once burned inside her. But as desires blaze white-hot, will Legion run again? Or will the unlikely pair succumb to love at long last?