The beloved / J.R. Ward.

Enhanced descriptions from Syndetics:

The daughter of a legend finds the love of a lifetime in this passionate, heart-wrenching installment in J.R. Ward's #1 New York Times bestselling Black Dagger Brotherhood series.

Nalla, the blooded daughter of Zsadist, has led a sheltered life. Protected by her father and the Brotherhood, kept away from the deadly war with the Lessening Society, she is chafing against the walls of the very safety that has ensured her survival. One night, she gives in to her restlessness...and finds herself face-to-face with a male whose inner darkness rivals even that of her sire's horrific origins.

Nate is a fighter with nothing to lose--and nothing to live for. Tortured in a human lab as a young, then cursed with immortality, he is all vengeance and no purpose because he cares for no one--not even himself. The Brotherhood knows this all too well and following Nate's deliberate violation of the cardinal rule in the war, they declare him a dangerous liability that must be dealt with.

When Nalla and Nate find themselves fighting side by side, daggers aren't the only things that fly. A sizzling attraction is ignited, though Nalla knows her sire will never accept him--and on his side, Nate has made a secret bargain to end his own immortality. As the enemy closes in, and Nalla realizes she must choose between her mate and her sire, what starts with such passion may well end with eternal sorrow and no chance of a reunion--even in the Fade.