When I was in a triad, none of us were married, so it was simple bf/gf type introductions. It didn't happen too often.
I don't quite like the "primary" / "secondary" titles since it shows the order you met people sometimes but not the intensity of the relationship. But it does seem to be pretty common and useful at times.
Introductions to family are fun. I am out to my family, but thay may have thought it was some fad I was going through.