Girlfriend wants to get married

Me and my girlfriend have been together 13 years. We have 2 kids together that are 11 and just had another baby. I have no interest in ever getting married again and I told her that when we started dating. I've been married once before. The marriage lasted barely a year before I filed for divorce. I got burned. Hard. My ex wife also made it hell to divorce her. Tried to get alimony from me even though the marriage barely lasted a year and it ended because of her. Something fucked up happened in our marriage and I left. She also kept trying to appeal the courts decision because they decided I did NOT owe alimony. She got fired from her job like 3 months prior to the divorce and felt like I owed her alimony because of that. The marriage ended in a nightmare and she made my life hell for 3 years after. I never want to get married again. I know some people have the point that it protects her but we both work. She also makes almost 30k more than I do a year so if we ever DID break up she wouldn't be left with nothing. I would be more screwed than her and I'm fine with that. The things that my ex wife put me through burned it for me. I'm fine without ever getting married again and she was fine with that up until recently. We went to a wedding and she started saying she didn't mind the idea of getting married now and she really would like to get married. I'm not interesting in marriage. I mean you could practically call us married now. I feel like marriage just causes things to do down hill. My mom said before she married my dad their relationship was fine. They got married and things went down hill. Me and my ex wife were fine. We got married. Things slowly went down hill. Then she did something that really fucked me up and broke everything. I've seen it happen with my friends. They're fine. Get married. Everything fucked up. I'm fine where our relationship is at. I don't want to get married ever again

Edit: I was upfront about never wanting to get married again. That was something I've always been straight forward about. It's not just my last marriage. My own father never to get married and I did and I got burnt by it. He told me marriage ends in misery and it did.