Dearly Beloathed series by Brigitte Knightley

Illustrated Hardcover Edition.  Book 1 is unsigned and Book 2 is physically signed.

The Irresistible Urge to Fall for Your Enemy--Book 1:

When Osric Mordaunt, member of the Fyren Order of assassins, falls ill, he realizes he needs the expertise of a very specific healer. As fate would have it, that healer belongs to an enemy faction, the Haelan Order.

Aurienne Fairhrim and her fellow Haelan are inundated by sick children suffering from an outbreak of a long-forgotten Pox. Unable to get the funding needed to launch an immunization program, the Haelan Order is desperate for money – so desperate that when Osric breaks into their headquarters to bribe Aurienne to heal him, she is forced to accept.

As Osric and Aurienne work together to solve not only his illness but the mysterious reoccurrence of the Pox, they find themselves ardently denying their attraction which only fuels the tension between them.

The Exquisite Torment of Loving Your Enemy--Book 2:

Osric is a member of the Fyren Order, a guild of assassins who gleefully murder for money. Aurienne is a Haelan, a scholar-healer whose Order’s motto is Harm to none. Clear-cut absolutes separate them: good and bad, right and wrong, light and dark . . .

Until they don’t.

When Osric first bribed Aurienne to heal him, he never imagined those lines would begin to blur. But every healing session draws them closer together. He finds himself developing unwanted feelings for Aurienne as her capable hands heal his body—and his heart.

Aurienne’s perfect life has been flung into chaos in the form of a devastatingly handsome assassin. She should be in her research lab, not illicitly healing a Fyren every full moon—nor wrestling an attraction to him that threatens to slip into something else.

Things go superbly sideways when Osric and Aurienne discover more about the deadly Pox deliberately unleashed through the Tīendoms. The plague may be the work of another Order—an Order far nastier than either of them can handle.

As the lines between Osric and Aurienne continue to blur, the balance between peace and war, and love and hate, trembles, shifts, and hinges on a heartbeat.