The Blood in Our Veins (Scars Eternal #1) by Anna Lyvis:
 
When Jessamine Vinca finds herself unexpectedly having to take care of a twelve-year-old boy, she's unsure how much her life is about to change. She certainly isn't expecting to end up living with the leader of the local enclave of vampires while protecting that boy from a religious cult. Callidora, the vampire leader with a penchant for knives, tests Jessamine's patience and restraint whenever possible, resulting in more tension than either of them was expecting. But when their knowledge of their shared past is called into question, things change in a way neither of them thought possible.