Lady & the Vamp (Immortality Bites, Book 3)

Former vampire hunter Michael Quinn is living a nightmare: he's been turned into a vampire. His only hope is the "Eye"--a long-lost artifact that, once every millennium, will grant one wish to its possessor. Fortunately for Quinn, he has a map detailing the path to the "Eye." All he needs to do is find it, then he can wish himself back into humanity.
Janie Parker has made a lot of many mistakes in her life, not the least of which was getting tricked into working for a demon. Not only is the pay awful, but she has to successfully complete all her unsavory assignments or risk a torturous death. Her latest mission is to track a vampire who apparently knows where some stupid treasure is. No problem. Until she sees who the vampire is -- Michael Quinn, a man she's had a crush on since she was twelve years old. Too bad she'll have to kill him to get to the "Eye."
But Quinn and Janie are kindred spirits, and soon they're falling in love even though they're after what the other person is desperate for: the "Eye".