Rakka no Ouji to Goei Kishi

The one-eyed prince, Shion, is forced to flee his homeland after his brother's betrayal. To escape his pursuers, he sets out for the country of his late mother's birth. Accompanying him on this perilous journey is his loyal knight and childhood protector, Fey. But upon reaching a safe haven, Fey is suddenly removed from Shion's personal service and begins to act suspiciously.
"I will protect you with my life, Your Highness," he had vowed from the day they met, and Fey has always upheld that promise. Now, however, as Fey reveals an unexpected side of himself, Shion finds himself unsettled and unsure of what lies beneath the knight’s steadfast loyalty…

(Source: Tokuma Shoten, translated)

Note: Includes 1 extra chapter.