Tisak by Michelle Frost

The mage magic that saved them could also be their undoing.
Theon and his men escaped House Natas, only to face suspicion and unrest from the Shifter Resistance. Shifters don’t trust mages, even ones who freed an entire House from their bonds.
As tensions rise, Theon’s tenuous control on his magic slips further, until one outburst leads to an amount of damage Theon can’t bear. He must learn to control his magic before someone else he loves is harmed or the fire growing inside him burns him alive.
Luckily, Florin knows where to go. Unfortunately, going to learn control means leaving some of his men behind.
They may survive the battle of Tisak, but can their love survive mage fire and the difficult choices in their path?