Half-Blood by Jennifer L. Armentrout

You will kill the ones you love. It is in your blood, in your fate.

Seventeen-year-old Alex and her mother have spent years on the run from the Covenant, a school where the pure descendants of gods hone their powers and half-mortal teens like Alex trainto kill daimons for them. But when her mom is murdered by daimons and she has nobody else to turn to, Alex finds herself back at the Covenant, where she has two options: become a servant for the pures or work twice as hard as everyone else to catch up in her training.

The second option seems like an easy choice, but everything gets complicated when pure-blood Aiden volunteers to be her personal trainer. Because not only is Aiden gorgeous, but he also understands Alex in a way she'snever experienced before. Unfortunately, relationships between pures and half-bloods are strictly forbidden.
But falling for Aiden isn't her biggest problem. As she learns the true reason her mother whisked her away from the Covenant and daimons close in on the school, she must fight to stay alive. . .even if it's her fault those around her are dropping dead.