Stolen Star by Michelle Madow

They’re bound by love. Hunted by fate. And the only way to save the world… is to survive each other.
After surviving gods, curses, and a kiss that fused their souls, Sapphire and Riven are finally united.
In name. In power. In purpose. In marriage.
Their mission now is clear: travel to the Summer Court to solidify a political alliance, gather the forces needed to stop the Night Court, and rescue Zoey from the hands of the enemy before it’s too late.
But nothing about this journey is safe. Not the assassins hiding among their own guard, and certainly not the secrets lingering between them.
Because Sapphire is haunted by visions of herself as a killer, standing over the people she loves. And Riven, once the cold and calculating Winter Prince, is unraveling in his love for Sapphire after she brought him back from death by fusing her soul to his. The more his feelings consume him, the harder it is to lead. And if he slips, he could destroy everything he’s trying to protect.
Together, Sapphire and Riven are stronger than ever.
But strength doesn’t matter if they can’t navigate the intense bond that links their souls—one that could either save them or lead them both into darkness.