I like what U dog says; it's very much like that.
What hubby likes to say is that we're married because we not only love each other, but LIKE each other a lot (LOT!), and we want to be together. We want to be around each other. All. The. Time.
That's a good reason to get married.
Before we married, I always thought that the real covenant was the commitment shared and expressed between the two persons in private vows. I was astounded by how very different life became once we shared public, and publicly, socially, religiously, societally ACKNOWLEDGED vows in addition to our private commitment.
I considered us an inseparably linked, exclusively committed unit the day we got engaged. But once we were publicly and socially 'married,' oh my god, was there another level of experience! There is a whole 'nother thing out there: a level beyond even the resolve of the two persons involved. When your whole family, social group, community and government recognize that you are 'married,' it is a completely different experience - for me, I felt it as an emotional-kinesthetic alteration in the way I live in the world. Perhaps an analogy would be like it's the difference between stepping into a bathtub versus stepping from a beach into the ocean. It just feels really, really different and far more expansive. Or at least, it does to me.
Once I experienced that transformation of 'being married,' I understood that marriage equality for all couples is important Not Only philosophically and Not Only from a practical standpoint of requiring access to partner visitation in hospitals etc., but also from a psycho-social-emotional standpoint of true belonging in the greater community of life. There is something sacramental about even the civil marriage license. Perhaps that's what bugs those who think gay couples should not participate, though I shall never understand wanting to deny any couple such an integral part of community life.