Cursed By Darkness by CM Haines

In a land plagued by darkness, she may be their only saving light.

After a tragic past, King Bodin refuses to let anyone near his heart, but he’ll do whatever it takes to save his people from this never-ending war. Even if that means agreeing to an arranged marriage, trading riches for soldiers and a princess who’s been hidden away most of her life.
Despite being sent to a man most fear, Princess Juniper knows this might be her only chance to escape the shadows. Especially when she discovers a room in her new palace full of portals to magical lands and Bodin gives her the keys to all but one.
She enjoys her freedom to explore, yet she can’t stop wondering what’s behind the mysterious door he won’t let her open. They might have formed an unexpected friendship, but there are still so many secrets between them.

Deadly secrets that could bring devastation to the few people they truly care about, including one another.