As a World Tree, Fey could see beyond all the people who were born in her world. After all, she was the mother of all beings living there. But when she looked at Dante... She couldn't see anything anymore. When she first met him, she had seen his entire being, and so she assumed that marrying him would be an opportunity for mutual benefit. But now... She no longer knew who this man was.
She already knew Dante was strong, but now her eyes, which could see beyond everything, couldn't find that Dante she knew.