Blackthorn by Nancey Cummings

The monster’s widow and the monster.

Alone for too long, the last of vampire Draven’s humanity is slipping away. Needing a mate to anchor him and keep the monster at bay, he strikes a bargain with a young hunter to find him a bride.
Newly widowed, historian Charlotte is desperate for a fresh start. When she’s presented with the unusual proposition of becoming a vampire’s bride for a year, she cannot pass up the chance to speak with one of the oldest creatures on the planet.

Charlotte unwittingly married a monster once, and it ended in disaster. The question is – will she knowingly make that choice again?