Blood and Lotuses — Teresa Noelle Roberts

When love is outlawed, only the bravest lovers can defeat an inhuman foe.
A demon in the guise of a goddess is “purifying” the great city of Dakura by killing off its stores of love, desire, and beauty. Once the city is void of color and passion, the demon can claim the city for its base to conquer the whole mortal world.
Anchali, a priestess of the goddess of love and desire, infiltrates the temple of the false goddess, along with her reluctant guardian Thanom, a soldier whose wife was murdered in a demon-inspired purge. They're hoping to get information to pass on to a rebel general who hopes to roust the cult from Dakura. What they find, though, tells them this isn't a job for warriors.
It's a job for lovers, using the power of passion to enact an ancient ritual.
Anchali can perform the ritual. But first she has to convince a broken-hearted man to love again.
Compared to that, defeating a demon is child's play.
Warning: Contains more explicit violence and less explicit sex than usual in a Teresa Noelle Roberts novel, along with all the magic and romance you've come to expect.