Thir and I are up against one of those official idiocies that says two have to live as cheaply as one, but only if they are legally married: so we can't afford to. One reason marriage is a dying institution.
But in my two previous marriages, the decision to make it legal came long after we had become an item, and I recall it as being pretty much a concensus reached on practical grounds (in both cases, the main reason was that she already had a child, and being a legal husband avoided endless arguments when I had to take responsibility for the child), with as much romance as a share issue. I think my late wife was the one who actually said "We should make this official," I can't remember who it was the other time.
I've always been hopelessly unromantic, but I do appreciate romance when it hits me. If a woman asked me to marry her, I certainly wouldn't ruin a beautiful moment by saying "No, I should do that."