A commitment ceremony is basically the same as a wedding, but without signing the legal paperwork. This is actually how marriage worked originally. You would invite friends and family to a small event, declare in front of everybody that you guys were now a couple, and start a family after that. The purpose of the ceremony was to at least establish a social expectation that you two were official, and that social expectation would weigh on you to keep you committed through the hard times. If you offer this compromise to a woman and she insists on the paperwork, it's a sign that she's up to no good.