That Old Black Magick — Michelle Rowen

Reluctant witch Eden Riley knows that codependent relationships aren't good, especially when you're possessed by a sexy but troublemaking demon. Darrak's physical form makes good girl Eden want to go bad, but the constant itch to use the soul-destroying black magic she's recently acquired might force Eden to explore her dark side in an entirely different way.

And when her magic starts manifesting itself without conscious effort, both Eden's life and the possibility of a future with Darrak are threatened-since only one of them might be able to survive this...