The Lost Barinov Dragon by Lauren Smith

Tasha Bellamy never expected to get lost in a snowstorm in the Swiss Alps, nor did she expect to fall into a cave and find a sleeping dragon…literally.
One touch awakens the black dragon and he transforms into a gorgeous, ancient, Russian warrior named Vasili.
She soon learns that Vasili has been missing from the world for more than seven hundred years after going on a quest for a dragon stone. But the quest cost Vasili his mate, and driven mad with grief, he sealed himself inside the cave to die.
Tasha can’t help but be drawn to the stormy-eyed dragon shifter and soon learns that her future and Vasili’s are entwined with his far more than she ever could have imagined when he tells her they are possible true mates.
Unable to resist falling for the noble-hearted dragon who’s touch sets her body aflame with desire, she yearns to heal his broken heart, but a revelation of her past might tear them apart.