Hanma no Ryuukishi wa, Henkyouhaku ni Shuuchaku Sareru

In the Kingdom of Niels, where dragons fly, Kyle, a "half-demon" knight of demonic descent who can speak the tongue of dragons, has a fateful reunion with his past lover, Alfred. Three years ago, for reasons he keeps to himself, Kyle bade farewell to his boyfriend, though he has never forgotten about him. But Alfred, who had once been his direct superior, is now just a count of the borders, a margrave, while he is but an ordinary knight. Kyle also holds a certain secret, which he can never tell Alfred... Since he has no right to by his side, Kyle tries to distance himself from Alfred, but Alfred won't allow them to part―?

(Source: AlphaPolis, translated)