Heart of the Dragon's Realm by Karalynn Lee

Princess Kimri is used to betrayal. Her brother sold her to a king in

exchange for swords to defend his lands. King Tathan’s reputation is as fierce as that

of his mountain kingdom—where dragons are said to guard the castle walls—but the realms

are unstable enough without angering the mountain-king, so Kimri reluctantly agrees to

the union. When she arrives in Helsmont, the king promises her a year of courtship

before marrying—or parting ways. Before long, Kimri thinks she may find comfort, and

perhaps eventually love, with the stoic king. But the realms are more unsettled than

Kimri realizes, and she soon finds herself caught in the middle of a war between the

kingdoms. Can she count on her betrothed to take her side? Or will his loyalty to his

kingdom come before his loyalty to her?