Key of Iron and Fate by Katherine A. Darling

I have a problem, and it has wings.

When I encounter an injured dark fae in the woods, I cannot leave him behind to die. Instead, I save him. The next morning he’s gone, but he left me a peculiar gift. Now the dark fae, Cethin, owes me a debt and haunts my every move, not to mention my thoughts.
I have more important things to worry about than the alluring fae. The transition of power from the current Lord of Sídhetír to his seventh son, Oren Byrne, is happening, allowing fae to pour through the gate between realms. As the former ward of the Byrne family and close friend of Oren and his six elder brothers, I want to help him through this time, but Lord Byrne orders me away from Oren’s side and I have no idea why.
As blood spills and deals are struck, I must work with Cethin to protect the Byrne family while trying not to get distracted by my ever-growing feelings. When secrets come to light, I am forced to make a choice that will change my life and maybe even the whole of Sídhetír.