Origins of Eternity by Nicole Pyland

After a three-century-long love affair that no longer feels right to her, Iro Black is ready to say goodbye to the vampire who turned her. She gave up killing, feeding on humans, and any kind of violence years ago, but Cassia, the woman who made her a vampire, still revels in it all. When Iro moves from Paris to Washington, DC, for her business, she lands in a bar one night, expecting to have a drink and go home alone, but she meets a woman who will change everything.
Arwen Lam only goes out with her best friend because Zara has something important to talk to her about, but before Zara can bring it up, Arwen spots the most beautiful woman she’s ever seen, and when that woman offers to buy her a drink, Arwen simply cannot refuse.

What follows is the story of Iro leaving a life with Cassia behind to begin a journey of love with the woman she was always meant to be with, but Cassia, of course, is not ready to let go. She keeps her eye on Iro’s budding romance with a feeble human before trying to stop it once and for all and finally have her revenge.