Bound By Treason by Eliza Tilton

A Mysterious Death. A Forbidden Romance. A Reign at its End.

When her third daughter mysteriously dies, Queen Moira will do whatever it takes to discover the truth and keep her youngest safe. She’s lost three children in the span of a year and will not lose another.
Her husband, the dragon king of the fae, had long left her chambers and found solace in his wicked mistresses who eased his erratic fears. He would not help Moira in this quest, and so she turned to the only fae she trusted: Tallis
Tallis, the head of the royal guard and her dear friend, would do anything to protect his queen and the royal line, but as the two fae search around the castle, they discover the truth behind the murders, and bringing the culprit to justice will tear the kingdom apart.

With each passing day, Moira is forced to choose who she is loyal to: the crown or her heart, because she can no longer honor both.