The Vampire's Pirate - The Immortal and Illicit Duology, #1

Is death too great a risk when the reward is freedom? Dáire Malone has been undead for over 200 years when he is summoned to the home of a would-be queen, a vampiress who possesses an unnatural potency. She declares that Malone will not leave without giving her a pledge of loyalty. He's been held in thrall before and would rather face his final death than let another have power over him. Thomas Clifton is a pirate, or rather, a privateer.
He too is summoned to the vampiress's home and commanded to pledge his fealty to her. Clifton's allegiance lies only with the man he sees in the mirror, and his first impulse is to run. But Dáire Malone's aura of mystery and his melancholy beauty appeal to Clifton, and Malone won't leave until they destroy the source of the vampiress's magic. Caught between opposing impulses, Clifton must choose. Leave, and lose Malone, or stay and risk his freedom.and his life.