I'm married, have been for 43 years. So it's a bit late for me.
I was just exploring the principle. Things were very different when I was young.
For a woman to have a child out of wedlock was very serious indeed. Today they don't seem to be bothered by this. I do know a few who don't even know just who the father is.
Well, I am probably as old as you and I knew girls in the 70's who did not know who the father of their child was. That is not new. But really, my answer would have been the same in 1970 as it is now, if you can't keep it in your pants, or the female version, if you can't keep your pants on then don't waste the time, emotion and money to get married. But then I grew up with parents that did not get along, dad had affairs and seemed to hate us. He was miserable but my mother insisted that she would not divorce him. When I was 13 I told her to throw his stuff in the street and change the locks and she was shocked that I would come up with something so mean, but he was miserable and made sure we were too when he was around. She was usually not present, even when her body was sitting at the dinner table, she was not there. It was a bad habit she started when she was a kid and could not handle the stress of what ever, so she actually was miserable too. If kids are involved they are better off with two separate but happy parents than two miserable together parents.
But even if there are not children, there is no rational reason to be married (legally responsible for ...) If you are not going to stop running around with other people. It is insanity, society is not requiring people to marry and procreate nowadays, and procreation has always happened outside of marriage and cause a lot of pain because of societies rules.
And, no matter what someone thinks, if they marry another there are expectations, even if they think there aren't.
Another edit: Emotions cannot be taken out of the equation no matter how much you want to.