I don’t think it’s unbelievable at all. As mentioned, the mom is a hoarder, which occurs as a result of or in tandem with other mental health issues. Judging by the poor state of her teeth, she’s probably had a lot of struggles, and if she is working, it’s likely not much more than minimum wage. He obviously loves his mom and wants to help her, but also probably doesn’t want to upgrade his apartment and lock into a permanent living situation. Right now, the space is small, and there are lots of animals, so the hoard is pretty under control, but with her own room, it would likely get out of hand quickly.