Osvald actually lives with a roommate in a rundown apartment and not with his parents. He's almost a young adult, and his parents agreed to let him have some extra freedom early. This is perfect for Mira, who has a bad experience with parents in general - and it means they have a place to throw lots of parties.
https://i.imgur.com/eF7b0mp.png
https://i.imgur.com/vb8ClFv.png
Mira's only problem with these parties is her jealousy, that kicks in whenever Osvald talks to another girl.
But he is aware of her feelings, and they usually manage to sort it out.
https://i.imgur.com/mO9WAoY.png
https://i.imgur.com/APp4RTm.png
The apartment is not big, and neither is Osvald's room, but there's room for Mira there whenever she wants.