As Oda Sakunosuke lay bleeding out in Dazai’s arms, he tells Dazai to become a good man and live a good life.

but Dazai didn’t do as he asked. All the people he killed. Everyone he has lost. It’d all be worthless.

So it seems he came into work the next day, utterly shattered and empty, completely different from what everyone usually sees in Dazai. What occurred effected him deeply and he went home early, which got you worried. so you show up at his door after you finished work.