I'm interested in this thread, as it's a question I've asked myself. I've been with a woman going on three years. We've been living together on weekends but are going to move in together in a couple months. That's going to be a big step for me to get used to right there. I really prefer sleeping alone and like my alone time. I'm a writer and keep abnormal hours. But I do feel that I've found the perfect woman to fit me. We get along so easily, have never been in a fight (we'll see if that continues once living together full time) and align in what we want out of life. In our minds, we are already committed for the long term. But we don't want kids, so what's the need to marry? Marriage as an institution means nothing to me. I'm not traditional in any beliefs. She also isn't the typical woman who grew up dreaming of her wedding day. I think she would like to be married to me, but really she just wants us to spend the rest of our lives together.
So if living together goes well, do we get married? That's the question that has crept into my mind. I don't think marriage is a requirement of hers for us to stay together. I've never felt any pressure from her in that regard. The pressure comes from my mother, the traditional old guard. She thinks highly of my girlfriend and has been urging me to propose for two years. Since marriage doesn't have the romantic connotations to me (who would consider romantic the most broken vows in the history of mankind?), the only appeal to me is of a business nature. I make a decent enough sum to comfortably cover my expenses and live relatively well, but she makes more than me and likely always will. She has a good job in business. As a writer, I sacrifice money to do what I enjoy and never have to work out of an office or for a boss. I do have more money than her, though, as she still has a little bit left to pay back in college loans while I'm nine years older and have had more time to save. If we marry, I can piggyback on her health benefits, which would certainly be a plus. People say there are tax benefits. I haven't taken the time yet to look seriously into that, but it could be another advantage. But I think the biggest financial reason to marry would be my mother and stepfather. They are wealthy and I expect my mother would reward us for getting married, probably paying for us to take a great trip ("honeymoon") and giving us money toward the purchase of our first house. If we got married, I expect it wouldn't be with a wedding. We aren't traditional or religious. I'd say we sign the papers, have a nice dinner with about 30 family/friends and then take it to our favorite bar. The possible financial downside to my getting married is if I get a 7-figure inheritance from my mother, and then we end up getting divorced. That's hopefully a long way from being an issue, and I really feel we are lifers. But I suppose that is what everyone thinks when they get married. At this point, I like the idea of building a life together and taking advantage of the increased buying power of our joint finances. I do see us as stronger together. My family's connections can help her make more. She can bring in more annually while I'll bring in more eventually. It looks like a boost to my short-term finances. I really want us to do this (build) together. I see this working because I see us working. Maybe this is naive.
So there's my thoughts. If you're going to have kids, I can see marriage being a way to provide a stable environment, even it is a mirage. If you're not having kids and you find the right woman who doesn't hold the traditional regard for marriage, I don't think it is needed to be committed to each other. If it's financially advantageous, why not? But I'm guessing the OP is looking at it as potentially harmful to his finances. And I'd say most guys get married for a combination of it being what they are supposed to do and the only way they can keep this woman they like in their life after a certain point.