I don't like to be nit-picky, but it is normal for people to fall asleep in the middle of conversations? I guess if the author is running out pages it is... kek.
@PTRB She could be faking being not tired and Koutarou assuming she is doing that so the lie works. Well, dunno, i just tried to answer your question on people suddenly fall asleep during conversation.
@seitann Their current situation are make go to beach is too luxurious, maybe for part time job is possible.
Now I think again this manga and Bokuben have MC from poor family, usually romcom manga have MC from middle high class family never worry about money and doing ecchi with his harem everydays.