Books 1-3 of the Bound Together Series.

Undeniable, book 1
Years after the Great War between the humans and vampires, the world is a very different place. Humans live under the rule of vampires, often becoming little more than slaves or personal blood bags. Ariana and her brother Chase have managed to live off the radar for twenty years with a small pocket of other humans, but when they are caught and forced into Vampire City, everything changes.

Inevitable, book 2
The bond between Ariana and the irresistible Vampire King, Alexander, transcends the physical and makes avoiding each other nearly impossible. Although, that is exactly what Ariana is trying to do. Unable to get past the horrible things Alexander has done, she pushes him away, convinced that being apart is the only way.
But fighting the inevitable is a battle she can’t win.

Unavailable, book 3
Dex wasn’t looking for a distraction, but it’s exactly what he needs, and he finds it with Ari’s best friend, Kaia. Kaia is a spunky little human, who is openly hot for Dex. There’s nothing complicated or wrong about being with her. She wants him, even if it’s a no-strings, sex-only thing, and he is all too willing to give her exactly what she needs. The problem is, Kaia wants more and Dex wants to be able to give it to her. But how can he be with her, knowing he can never offer her more than half of himself?