I went back to the beginning and reread this really don’t know why he’s dating her.
She insults him all the time, and in ways that exclusively target the things he feels most insecure about. Really hurtful treatment throughout. She’s very dismissive of his feelings, manipulative, and clearly revels in their dominant position in their relationship.
She asked him if he’s afraid of her and I think it’s obvious that he is, especially now.
So what is he getting out of this? It’s sad to say, but it’s probably not much more than the illusion of ‘protection’, but it’s more like he’s a possession than a cherished partner.