Kare no Hatsukoi wa, Doku ka Aruiwa. His First Love, Poison Or.

Synopsis

It's been ten years since Miyako fled from his feelings for his childhood friend. Only the invitation to their wedding brings the two back in contact with each other. While Miyako is still trying to finally forget his unfulfilled love, another man suddenly appears on the scene. Yuuya, the younger and most attractive brother of his childhood crush, confesses to Miyako his years of affection, and thus ignites a storm of old and new desires... (Source: KAZÉ, translated)