The Bed Wife By Suzanna Lynn
Here is the synopsis of the book:
The Bed Wife Chronicles: Love brought them together. Would tradition tear them apart?
Once inseparable childhood friends, Luana and Baylin are now grown and in two separate worlds. Luana, the daughter of the town drunk, overlooks her family’s goat farm to make ends meet. Baylin, Prince and future King of Grasmere, is off combatting the veils that lurk in the Kingdom.
However, fate intercedes with a time-honored tradition that has been custom for the past five hundred years. Luana’s life is now forced into the hands of her long-lost childhood friend. Will resentment, hurt, and duty consume them? Or will Luana and Baylin find love and rekindle their friendship?
Here is the GoodReads link to the book: https://www.goodreads.com/book/show/21503293-the-bed-wife