What is the ruling regarding a spouse saying to the other, "May Allah curse you," whether in a state of contentment or anger, and what are the consequences of that?

It is not permissible for either the husband or the wife to curse the other under any circumstances. The one from whom such an act originates must repent, show remorse, and seek forgiveness. This curse does not affect the marital relationship in terms of divorce or ẓihār.