Alyson Noel: Shadowland

It is the third book in the Immortals series. Ever has a problem, any contact with Damen will kill him. In this book she has to figure out how to reverse the effects of the "antidote" given to Damen to make him healthy again.
Ever and Damen have traveled through countless past lives - and fought off the world's darkest enemies - so they could be together forever. But just as their long-awaited destiny is finally within reach, a powerful curse falls upon Damen...More...

It is the third book in the Immortals series. Ever has a problem, any contact with Damen will kill him. In this book she has to figure out how to reverse the effects of the "antidote" given to Damen to make him healthy again.
Ever and Damen have traveled through countless past lives - and fought off the world's darkest enemies - so they could be together forever. But just as their long-awaited destiny is finally within reach, a powerful curse falls upon Damen... one that could destroy everything. Now a single touch of their hands or a soft brush of their lips could mean sudden death - plunging Damen into a bleak afterlife in the Shadowland, an eternal abyss for lost souls. Desperate to break the curse and save Damen, Ever immerses herself in magick - and gets help from an unexpected source... Jude Knight.
Although she and Jude have only just met, he feels startlingly familiar. Despite her fierce loyalty to Damen, Ever is drawn to Jude, a green-eyed golden boy with magical talents and a mysterious past. She's always believed Damen to be her soul mate and one true love - and she still believes it to be true. But as Damen pulls away to save them from the darkness inhabiting his soul, Ever's connection with Jude grows stronger - and tests her love for Damen like never before...