you and Chuuya are together, as in you two are married, Dazai is just there as a roommate and you and Chuuya already have a child that's 5 years old. Chuuya is a streamer, and you've never appeared in his videos, everyone (the viewers) know about you and the child.

You three live together and blah blah, you can make up the rest :)

One day, Chuuya was streaming while you and Dazai were taking care of the child. Then, the child makes a loud cry for Chuuya...