Aloha: My partner and I wrote a "commitment contract" at the end of our first year together. It is a 5 page document outlining our commitment to each other and the fact that we are open to expanding our family and having other lovers. The contract was originally good for one year, cancellable or automatically extendable or modifiable as desired. It was printed on nice
paper and bound in a folder.
We had a big party (friends and family and former loves) and read the contract aloud. We then passed it around and everyone signed on the the pages they chose. We had not told anyone in advance of this part of our party (it was a housewarming/anniversary party) and we got great response.
I am the keeper of the contract along with the cards and memorabilia from the party. Though we had planned to renew it annually at a party, we are always too busy. Now we have just started our fourth year together. Maybe at 5 years we will do it again. In the meantime, the contract serves as a reminder about our higher selves in the relationship and occasionally I remember to read it and realize I am violating the spirit of it when I am unconscious in relating with my partner.
Neither of us wants to marry, though once in a while one or the other of us "gets that urge." We are libertarians and don't feel the state has any business in telling us who we can or cannot marry. If there were compelling tax reasons, we might do it, but there isn't.
So, our commitment was "public" and "private" and we tell anyone who asks that we have a contracted relationship. People seem interested. Finally a personal commitment is the first necessary ingredient.