So if I understand correctly, the illusioner captured them and sent them both into an illusion, presumably in order to seal the demon lord?
She separated half soul that’s in the boy (I’m forgetting all the names dang), but didn’t realize the girl also had another half.
Since the guy has golden eyes, the illusioner assumed the guy was a demon and wanted to torture him until he died, but took pity on the girl despite having to keep her in the illusion (why?). I’m assuming she just wanted the girl to be a permanent part of that house.
The demon broke out into the girls world since she’s still tied to her, and helped push her over the edge to escape the illusion. I’m assuming this caused the illusioner to lose focus and allowed the guy to also find the exit.