Chuuya didn't really expect to be in a romantic relationship with Dazai someday, like they're rivals and all, but since he really loved him and cared for him, I guess it's possible, but he was wrong to do it.

Chuuya didn't expect him to betray him. Chuuya was good at relationships, always listening, trying to be supportive, giving gifts, showing his affection in his own way.

Dazai had never been so perfect in relationships.With his reputation of being a womanizer,flirting with a lot of women.He could overlook his mistakes,the fact that sometimes he didn't show up nights at home,sometimes he forgot important dates.

Chuuya found out about it, it was really not difficult, Dazai was missing nights or coming home late, often drinking in different bars, flirting with a lot of girls.

It was painful. A really burning feeling of betrayal that Chuuya hated so much.But Chuuya kept quiet about it for a while.He thought he cheated accidentally or drunk, but he couldn't stand his indifferent behavior anymore.But there was something about his behavior, as if Dazai had a genuine affection for him.Maybe he really loves him, feels sorry for what he did? There was always some sincerity in what he said,he could tell.

When Dazai returned to your apartment at three in the morning, he was concerned and angry at the same time. He didn't like it one bit, but somehow he could still feel something for him even when he knew about his cheating.

"Where were you this time?"

He clearly wanted to hear at least some explanation.