"Married" means priorities have been set.
We have been married for just about three years, together for six and a bit. We met when we were both with mono partners, and had negotiated being open. We were lovers for several months, and then realized that we wanted to build a future together as primaries; needless to say it was a massive transition for both of us.
We were monogamous for the first four years of our relationship. We've been open for over two years in various forms; a few triads both casual and more serious, a quad, and some dyads. I don't think that either of us would consider ever permanently closing our relationship; I don't even know if we were under that impression of being closed prior to opening - it was just what felt right at the time. We've folded back into monogamy a couple of times, and find that satisfying as well - it's largely about having the freedom to explore if and when we want to, more than anything. Non possession, but we have set each other as 'priorities' through marriage. Neither of us have ever really desired strictly monogamous relationships in our pasts.