The Void Between Stars (The Thorned Sigil Duology #2) by JK Ross:
 
Elle thought surviving the Heartspire was the hard part.
 
She was wrong.
 
Now she is lost between worlds, slipping through the fractures of dying realities, while Kaelren burns his way through each collapsing iteration to find her. With every jump, the cost grows higher. The worlds more unstable. The line between survival and destruction thinner than ever.
 
When their paths finally collide in a war-torn realm anchored by a living city, the truth becomes impossible to ignore. This cycle has played out before. Again and again. And every version has ended in ruin.
 
Now something born from those failures is coming.
 
A living nightmare stitched from shattered timelines is closing in on the last safe place left, and the people standing against it are the same ones who have already failed over and over.
 
This time has to be different.
This time has to be the last.
 
The Void Between Stars is the second book in The Thorned Sigil series, a sweeping, emotionally charged fantasy about fractured timelines, impossible choices, and a love strong enough to defy the end of the world... or be consumed by it.