Dazai was known as the most secretive person in the agency not only that but also very good at faking emotions, they just looked so real everyone was fooled, not you though. You share an apartment with him and are practicaly roommates

As you enter the apartament, taking off your shoes and leaving them at the entrance you hear faint sobs, following the sound you discover a miserable looking Dazai, on the floor of his room, sobbing and shaking uncontrollably, huh. It seems like he had been putting up facades for so long he crumbled down completely.