Time Out of Mind (Cora's Bond Vampire #3) by V. M. Black

In the Third Book of the Vampire Serial, Cora Discovers a Darker Side of Dorian's World... Cora Shaw was bonded to billionaire vampire Dorian Thorne twice—once by blood and again by choice.

But with the death of one of her best friends, she discovers that her choice was far more dangerous than she ever expected. Everything is falling apart, from her role in Dorian's research to any sense of normality remaining in her ordinary life. And as the stakes keep getting higher, her wedding day grows ever closer.