He is already married to her. If she is outright disrespecting him because she now makes more than him, then divorce her. No need to worry about alimony, she makes more money. Her changing up after she made more is just an expression of her very own low character. He should have been able to suss that out of her before he married her, but it is too late now.
He can always work towards making more income in various other ways after he divorces her. He does not need to run to try to fix the situation now, since she has already shown to him that her respect of him was incumbent upon him remaining the greater breadwinner in the family. So she only respects and perhaps loves him for what he could do for her. Once she felt she could do better than him, she also felt she no longer needed to respect him. No self-respecting man would sit around for that. He can make more later and vet better later, while taking this all as a learning experience.
*This is all said about the situation described, with the fact of it being true or not being unimportant.