These Bitter Blooms by Emma Hamm

In a world where magic means power, a “small” gift is a curse.
Thea was not blessed with power. Her gift of devouring plants and absorbing their hidden abilities does not make her stand out among her peers. Until a young man from the other side of the river sees something in her that no one else has seen before. When his family mercilessly strikes at her pride, he makes a point to ease the sting.
Alistair is not like his family. He has no interest in magic or wealth. He can see through the veil of the world into the faerie realm, and that has no use in his family. He never understood the desire to write to the girl across the river, but she turns his world of grey into a life of color. At the first opportunity, he meets with her. The second, he falls in love. And the third, he knows he wants to marry her.
Until the cities across the river go to war. Their lives are shattered, ripped apart, and thrown asunder. Then, ten years later, a chance meeting brings them back together. He needs a secretary. She needs a job. Neither realized they were about to be thrown into each other’s arms once again. And this time, he doesn’t intend to ever let her go.