I think the reason some people responded the way they did is the use of the word "validly". Perhaps "legally" might have been a better choice.
A legal marriage is one that is honored or recognized by the state or the government. This can include common-law marriages in some US states and in many other countries (i.e., where the couple lives together for enough years to be considered "married" even if they never had a ceremony). A legal marriage has implications for things like inheritance, insurance coverage, and the "legitimacy" of children (which is a loaded term in its own right and illegal today in some places...but I'm trying to address many sides to this issue over time).
The word "valid" is subjective. What do you think is a valid marriage? What does your aunt think is a valid marriage? What does the state consider a valid marriage? When is a marriage invalid? What determines the validity of a marriage? Can a marriage be invalidated? This is all too fuzzy and confusing for our purposes here.
Personally, I think there should be a way to indicate a common-law marriage on WikiTree, because that is a legal form of marriage in many places. But it is not the only type of relationship that is "honored by the state" or is otherwise given legal protections under the law.
I think there could be something as simple as a dropdown option to describe the relationship:
- marriage
- civil union
- common-law marriage
- cohabitation
Of course, the exact wording would be determined by the context in which the label would ultimately be used.
I don't think that it matters what sexes the individuals are, nor does it matter their gender identity. There are a few types of "couple" relationships and I think we could find some simple, factual labels that apply across a broad spectrum of countries and cultures over time.