Joushi to Ore no Himitsu by Minase Masara

Summary

Plot: The love full of mistakes between my boss and me is about to begin?! Just because of a single mistake, my life is about to go through an unbelievable change. Drunken, Nagato Hiroki committed a mistake of one-night stand with a man who he barely knows! But, it was found out that his newly assigned boss, Kurosawa, is that man from the past he had one-night stand with!