from my pov, living with a romantic partner is a form of communal living.
That’s the thing, I think. I’m pretty confident that most people I know wouldn’t consider living with a romantic partner communal living, or even living with one’s own spouse and children to be that. It comes back to there being a qualitative difference in the relationships between friends, lovers, family members and partners. The relationships with family members and partners would allow for living together much more so than relationships with friends or even lovers. And communal living would very likely be conceptualised as living without those kind of relationships being involved.
I should emphasise that I’m definitely mostly speaking of Finnish people here, because those are the ones I know most about with regard to living choices and relationship outcomes. It is possible that my takes are reflective of how personal space and emotional distance is conceptualised in Finnish culture.