We have wills, of course, which we got when we bought a house together, as many people do (and then go on to marry)
Our wills are nullified if either of us marries. So we would have to get them drawn up again, in the event of marriage. That’s another cost of entering into a marriage. It’s not enough just to say, oh we are married now, everything will just go to the other. You do actually need to think about how things will be divided up, guardianship for your children, and contingency planning for the event of you both dying in the same incident. Even if you are married.
Going and getting married isn’t a catch all solution.
I’m not going to go and get married. However much anyone says, you don’t have to do dresses, rings, cakes, or call yourself husband and wife, change your name, etc etc, you do have to vow to take the other as a husband/wife. You do have to fight the assumption about what that means. You do have to enter the state of matrimony, knowing what it was intended for, knowing what it has meant to people in the past, knowing that you do not in fact want that for yourself. You do have to explain to people that yes you are married, but no he’s not your husband. And to your family, that yes you had a wedding, but no you didn’t invite them. And that yes you are married, but no your name is not Mrs Traitor. And that yes, your children have your name, and that yes, he is their father, and that, yes, you are married, but no, that is not illegal. You do have to face the problem of dissolving the marriage, one of you will lose out to the other financially, who is to know who that will be. There will be costs to getting married, some financial, some personal, some short term and some long term.
I care about my children. I support them financially. I ensure their future is protected. It would be a VERY bad idea for me to think of marriage. They would be significantly worse off.