Sleepwalkers by Daniel May

My immortal ex was the last person I wanted to be stuck in a coffin with, and yet here we were.
Broken up for over a century, I stayed in touch with Bonifacio out of necessity only. An amoral horndog and possessive leech, Bonifacio was toxic beyond words, but there was no one better at eradicating vampire hunters. I needed him.
But it was Bonifacio who slayed the wrong vampire hunter, Bonifacio that freed the evil spirit, and Bonifacio who forced us to flee to the only safe place we knew: the catacombs.
In those deep, treacherous tunnels under the city, I’m trapped with the man I hate most of all… and want more than anything.
With dreams reminding me of the Bonifacio I fell for and my waking moments tortured with his presence, I fight a war on two fronts. I must not only survive the catacombs’ secret, but also withstand my hunger, as old longing rears its head.
Bonifacio possessed me once. I must not let him possess me again.