Prince of the Damned by Ana Calin

Lord Vlad Dracula has just one weakness–his wife, Ruxandra.
So when a mysterious vampire tries to assassinate her, Vlad tears his throat open. But the vampire’s blood starts a strange process in Lord Dracula’s body, enhancing his killer instincts and making him dangerous even to the one woman he’d die for–Rux.
Dracula changes, his inner demons boiling to the surface–control, jealousy, bloodlust. His desire for Rux grows dangerous and suffocating, and his thirst for blood insatiable. Rux must unmask the invisible foe that drives her husband ever deeper into darkness, before his evil plan makes Dracula self-destruct. The question is–will she survive long enough to do it?