(Researchers) looked at men’s and women’s perception of their own feminism and its link to relationship health... They found that having a feminist partner was linked to healthier heterosexual relationships for women. Men with feminist partners also reported both more stable relationships and greater sexual satisfaction... Feminist women were more likely to be in a heterosexual romantic relationship than non-feminist women.
This seems true to me. However the relationship is probably not simply causal. I think it's partly a side-effect of the fact that people who identify as feminist are likely to be younger, better educated, in better paid jobs, and more likely to have 'optimum family size' for economic circumstances. Probably lower incidence of alcoholism, drug addiction and domestic violence too.
So my guess is that 'feminism' is a kind of lifestyle associated with other positive things. I would guess that anti-racism is probably associated with happier relationships, even where both partners are the same ethnic group. Reading books probably is too.
Having said that I do think men have a happier time in relationships where women are fairly outspoken about what they want, and think of themselves as equals. I can't prove it, but I have that feeling. So I think there is a causal link too.