Blood and Rain — Shira Anthony

Blood: Book One
Vampire hunter Adrien Gilbert never dreamed he'd fall for his prey or that his love, Nicolas Lambert, would give him the gift of immortality. But when a hunter bent on destroying the truce between vampires and hunters throws the gauntlet at Adrien's feet, Adrien must travel through time to save Nicolas, and with him, the entire vampire race.
Born in the 1800s into a clan of vampire hunters, Adrien once wanted only to tend his family's vineyard or read a good book. Then his older brother is murdered. Bound by his hunter's oath, Adrien sets out on a path that will change his life when he agrees to execute his brother's killer, the vampire Charles Duvalier.

After months chasing Charles, Adrien reluctantly makes a bargain with ancient vampire Nicolas Lambert. Adrien will escort Nicolas to Paris for his marriage to a rival clanswoman, and Nicolas will help Adrien find Charles. Nicolas's quiet strength and gentle heart soon convince Adrien that Nicolas is nothing like the vampires he has sworn to destroy. But as the wedding draws nearer, a sinister figure threatens the already fragile peace. To secure both past and future for those he loves, Adrien must find a way to stop the looming war. But first he'll have to let Nicolas go.