The Engineered Throne by Megan Derr

Lord Vellem is a man desperate for escape. His father hides from his problems in alcohol, his mother hides from her misery in drugs, and his brother fled to the relative safety of the royal palace. Vellem eventually found solace in the Royal Army Corp of Engineers, but still could not entirely escape. Then his brother provides him with an unexpected chance, and now Vellem's marriage to the young prince of a neighboring kingdom is only months away.

The marriage promises not just a fresh start in a new land, but a challenge to his famed skills in building roads and bridges. But before he can settle into his new life, tragedy strikes, and Vellem isn't certain he's up to rebuilding the ruin left in its wake.