Ghost by Grace Brennan

Damara Costas is the only female Enforcer in her crew, something she’s always taken pride in. Putting herself in jeopardy for missions is something she does regularly, but this time it’s different. This time, she might not make it out alive. There’s only one hope she’s holding onto—the mysterious man who lends her his strength when her own falters.
Jase Benson goes by many names, but right now there’s only one that matters—Damara’s protector. She’s everything he never thought he’d find, but will she ever forgive him for what he’s done in the past? All he can do now is protect her with his life and show her the man he truly is inside—and hope she can overlook the man he used to be.
The world is imploding around them as they race to rescue the last dragon and defeat the evil surrounding them, once and for all. And hell is breaking loose in Damara’s heart, as well. How can she love the man who betrayed her friend? And how can he love a woman who’s nothing more than a ghost?