Knightley, Brigitte. Dearly beloathed duology #1

"Loyalties are tested in this enemies-to-lovers romantasy following a healer and assassin from enemy sides who are forced to work together and find the source of two deadly diseases, all while resisting the urge to kill each other-and, just maybe, fall in love. When Osric Mordaunt, member of the Fyren Order, a society of assassins, finds himself sick with a degenerative disease, he needs the expertise of a very specific healer. As fate would have it, that healer is a member of his enemy Order, the Haelan. Aurienne Fairhrim's Haelan Order is besieged by the need to care for thousands of sick and dying children suffering from Platt's Pox, an almost forgotten disease that has suddenly reemerged with extreme virulence. Unable to get the funding needed to immunize the sick children, her Order is desperate. So desperate that when Osric Mordaunt breaks into her office to offer her a bribe that would completely fund their Order's immunization efforts, in exchange for her healing services, the Head of the Haelan commands Aurienne to accept. Despite being enemies, as Osric and Aurienne work together to solve not only his illness but the mysterious reoccurrence of the Pox, they find themselves ardently denying an attraction that seems only to fuel the tension between them"--