Kisei Shitara Juushi ga Kurashiteta - Ch. 2 - Hmm? I'm living here.

[MangaDex]

 

[DynJarren]

Dude went a month without knowing his cousin lived in his house, either he was away, is a neet, or his house is massive.

 

[Kaarme]

Dude went a month without knowing his cousin lived in his house, either he was away, is a neet, or his house is massive.

I reckon she meant the decision was made a month ago. Surely he would have noticed otherwise, unless he was travelling as well. But then again, the family seems to carry a strong airhead gene, so who knows.