To Bind and Break by Lisa Hayes

Hadrian has spent his life healing soldiers in a war he no longer believes in. When he discovers a wounded rebel left to die, he follows his conscience instead of orders and makes a choice that could cost him everything.
To Dorian, mages are and always have been the enemy. But the more time he spends with the strange magic user who healed him, the more his certainty gives way to questions he doesn’t know how to answer.
As the truths that once shaped their lives begin to unravel, and attraction grows into something deeper, two enemies must decide what they’re willing to risk to be something more.