The Siege Bride by Samantha Cayto

Being a bride is a state of mind, not of body.
Henry, Baron Roth, is laying siege to a Moorcondian duke who has proclaimed himself the new king of a separate country. Henry is tasked with the job of defeating the traitorous man and is prepared to wait as long as it takes, even if it means spending a boring winter in an increasingly hostile place. His luck turns when he discovers the duke’s son hiding among a group of local nuns. The pretty boy could hold the secret to ending the confrontation without a slaughter on either side.

Kellen has lived a life of indulgence, having no interest in politics and preferring to spend his time in pursuit of making wine. When his father comes under siege, a locked-out Kellen tries to escape past Henry’s camp. Instead, he ends up in the man’s imprisoning arms— a surprisingly comfortable place. His family loyalty is tested by an irresistible attraction.