King's Obsession. Obsession Series, #1

Centuries ago, an epic love story began between the king demon and a troll in the human realm. But can it survive when one lover doesn't trust what his heart knows, and before the other's patience runs out?Racked with grief, King Asmodeus enters the forest through a secret portal from the demon realm. When he encounters a troll, his life will never be the same again. How can Asmodeus trust something he doesn't understand? Despite his fear of their connection, he's unable to stay away from his troll.
Their connection is immediate, and he wants to know why that is. A quest that endures for centuries. Dougal has the patience of a saint, which comes in handy when nurturing both the forest he lives in and the love of his life. One encounter with Asmodeus is all it takes for him to understand what they are to each other-and to realize Asmodeus needs time to figure that out. When Asmodeus witnesses unequivocal bonds-blissful ones-for demons, Dougal decides he's had enough.
He issues Asmodeus with an ultimatum-accept what they mean to each other, or leave and never come back. Will Asmodeus come to his senses before it's too late?King's Obsession is the last book in the Obsession series, where trust can be the hardest lesson to learn, but it also brings the biggest rewards.