Akuma ga Kitarite Kimi ni Muchuu

Corporate slave Yuuto, under the influence of drunkenness, summoned the demon Morax. He made a contract with him where, in return of granting a single wish, Morax would receive his soul. Yuuto had used his wish to "become happy," and so began his comfortable life of ordering around a demon. However, Morax is the type of demon that feeds off of human bodily fluids and vitality. Because of that, Yuuto ends up having sex with him! They continue this strange cohabitation with a demon...?!

(Source: Frontier Works, translated)