Shapeshifter (2010)

Ben has always been troubled by violent nightmares about himself killing other people. Now they're getting worse and he doesn't know why-until he meets Nina, a beautiful woman with a secret-in the dark of night she can transform into a demonic killing machine known as a Shriven. Ben, she reveals, is also a Shriven and he is destined to become her mate. However, Ben is horrified to learn that Shriven must feed on humans in order to live.