The Spring Dragon (Dragos Primeri #2) by Natalie Wright:
 
What if your lover’s soul was taken by—a dragon! His youth was a tapestry of vows and oaths to gods he no longer believes in. But in Quen, Aldewin found once again someone in which to place his faith.

But then, a dragon took her soul and flew off to gods know where. Bested and feeling broken, the only thing that keeps Aldewin from giving up is his last promise—to protect Nivi, the snow tiger Quen befriended.

When old friends arrive with fresh news, Aldewin’s mandate becomes To restore the love he lost, Aldewin must find the legendary Heart of Menaris.

And, Aldewin must secure its power before the Dynasty, or he’ll lose all hope of ever seeing his lover again.