Threadbound by KM Avery

The moment he was born, Jamie Weaver was tied by the threads of fate to a fae prince—he just didn’t know it yet.
When Jamie moved to Edinburgh for graduate school, he wasn’t looking for adventure or romance—he just wanted to escape the monotony of small-town Tennessee and the constant anxiety of having to live with his step-father. The ancient city and even more ancient crags drew him in, and he immersed himself in his studies and the atmosphere of Scotland.

Bran mac Cairn still hasn’t come to terms with the fact that he’s been tied to a half-breed.
If he had to be one of the threadbound, tied to another by drawing his first breath at the same exact instant, why couldn’t he have been tied to someone powerful? Someone interesting? But no, Bran had to be tied to a completely ordinary-seeming human half-breed who had thus far spent his life in a place Bran wouldn’t be caught either dead or alive in.

The threads that bind them are growing impatient.
At twenty-five, all threadbound are expected to formalize their bond. But Jamie knows nothing about it, and Bran has no desire to be any more permanently attached to an annoying mortal than he already is. Except that he also can’t stay away.