The Sorceress Transcendent by Casey Blair

Once mortal enemies on the battlefield, what can they become supporting each other instead?
When Varius, the greatest general of the Aurelian Empire, is forced to flee his homeland, there’s only one person he can turn to.

A powerful sorceress and once his most deadly enemy, Theira is the only combatant who’s ever escaped the war between their peoples. But with the memories of how they kept each other going from opposite sides of a battlefield, when a bleeding Varius knocks on her door, she lets him in, even knowing what will follow.
Theira may have gotten away, but as long as the war goes on, she’ll never really be free. Now with both their peoples actively hunting them, the two most dangerous fighters in a never-ending war will have to join forces to do the impossible: end it once and for all, on their terms.

And if they can dare to dream boldly enough, maybe find happiness for themselves, too.