On the other hand, feminist relationships seem to be happier.

If both results hold, it could plausibly be that feminism and unhappiness are both caused by something else at the country-wide level (the collapse of traditional meaning and values, perhaps,) or that feminism improves intimate relationships while worsening other aspects of life (by increasing labor supply, perhaps,) or that feminists make things worse for non-feminists (by not laughing at their rape jokes, perhaps.)