Rhavos by Alana Serra, Juno Wells

As his enemy, he’s honor-bound to destroy her. But as his mate, she might just destroy him first.

Ren Alvarez doesn’t remember the last five years of her life.
Taken hostage by an anti-alien terrorist organization and forced to write malicious code to target the Karuvar, she hasn’t been in control of her own destiny–or even her own mind–for a long time. When a massive, brutish, sexy-as-hell Karuvar warlord storms the base where she’s being held, she doesn’t know her salvation has arrived. After all, as far as he’s concerned, she’s the enemy. It doesn’t matter that he keeps saying she’s his mate.
As Conqueror, Rhavos has spent his life eliminating threats to the Karuvar and bringing other, lesser species to heel. A group of rebel humans should be an easy problem to solve, but when he finds his mate among them, Rhavos does the one thing he swore he’d never do: He hesitates.
To have any hope of bringing down a common foe, Rhavos and Ren are forced to trust each other. For the first time in her life, Ren learns to rely on someone other than herself, placing the protection of her mind and body in the very capable–and very talented–hands of an alpha male who would eviscerate anyone who even looks at her the wrong way.
But even the strongest bonds will be tested as the Karuvar face a new threat. And when tragedy strikes, Ren and Rhavos are put to the ultimate test: Betray their people, or stand together no matter the consequences?