Song of Dragons by Aja James

Every lore of every clan, across time and space, dreamed of dragons. Did you ever wonder why?

Erebu and Sorin fought through countless lifetimes of trials and tribulations to find one another again. They even conquered death.
But Ere’s rebirth requires a price: he must answer the Celestial Summons when it comes and faithfully complete each task the Jade Emperor sets before him.
On the bright side, he doesn’t have to perform miracles alone. Sorin will be right there with him. One the not so bright side, his Fate, the Fate of all dragon Kind, and by extension, the Universal Balance, depend on the successful execution of each quest.
No pressure.
His second task is find and retrieve the Song of Destiny.
Location: Unknown. Time travel will be required.
Clues: Too few. But there may be a few harpies, a centaur, a giant Chinese Tibetan Mastiff and other mythical monsters along the way.
Accompaniments: His beloved Sorin (who is all he needs!) A spoiled, vain, high maintenance she-dragon (who he doesn’t need). But whose enchantment spells have their uses from time to time.
Timing: ASAP. Determined by an arbitrary Sandglass in the Jade Emperor’s possession.
The end of the world may be just around the corner. Along the way, enemies may become lovers, reluctant friendships may form, and lots of hot, desperate, this-may-be-the-last-time-we-have-sex sex will definitely be had.
And who knows, you too may fall under the enchantment of…