From Tortured Fates by Anna Hawke

No one is safe from the monster inside their head.
Abducted by an organization that's pledged to eradicate all immortals, Lucius is robbed of more than just his freedom. Tortured and blinded, the volatile predator within him surfaces, bringing with it a wave of bloodlust. After an eternity of torment, he's given up on being rescued-given up on staying sane.
Though she's young, Circe's unique tracking ability allows her to find the vampire elder when all hope had been lost. But finding him isn't the hard part-it's keeping him alive. As Circe heals his devastating wounds, her soul stirs, drawing them together with a fated mate bond she never saw coming.
His abductors stalk the shadows behind them, determined to recapture him. As Lucius begins to succumb to the poison in his veins, the starving predator within becomes more ravenous-and it's her blood that calls to him.
After all, a starving vampire is a dangerous one.