A Cruel Kindness by Rory L. Scott

A Cruel Kindness is the first in a series following an overarching plot over the course of standalone love stories, and is a Soul Mates, reluctant allies, forced proximity romance full of fantasy and science fiction elements.

The Bridge. The fabled connection between two sister planets, able to send people through time and space to reach the other. A story of harmony between worlds ruled by the same gods.
The reality was a war, twenty years and counting, with one planet fighting to keep the other from invading their world. Their strongest weapon—the paranimas. The Soul Mates.
Able to hop between worlds at a whim, the few blessed with a perfect match for their soul were trusted to protect their planet from the threat of the other.

The next pair blessed would test the old adage that Soul Mates fell in love with one another at first sight. Shoved together despite years of hatred and betrayal between their families, Bellamy and Soren must cross the Bridge and put a stop to the war, no matter who is really at fault.