The Qualm Before the Storm by Lilo Quie

Rayne has never been close with his family, never found love or even someone who understands him. He finds himself graduating college at the tail end of another bad breakup and needs to get as far away as possible. A thousand miles away sits the most striking horse he’s ever seen, and he cannot resist petting it. Now he’s stuck with a god, but he’s not too mad about it. Especially since he gave him a pet chicken!

The Tempest Spirit has wandered this world for over a thousand years. He has changed his skin and species more times than he can count, but none of his loves tend to live long, for a god. His worshipers grow fewer by the day and he thinks about moving on, joining the sky as storm, or as the wild mustangs that wandered this land so long ago, their hooves bringing thunder. When the most curious human shows up in his paddock, he thinks he might stick around a little longer. After all, he can feel the Rayne coming.