Married, merged finances.
Advantages aside from the economies of a household of two are mostly structural in the law, but they're more extensive than most people think about: my much better insurance through work (cheaper by far for me to insure us both and for us to meet the max out of pocket than for him to pay his premiums through work...), my pension, which will include health care coverage for us both (he has a pension, but it doesn't include health), and the general ability to take care of "stuff" however conveniences us most.
For example, we bought an empty parcel next to our property a couple of years ago, and it's still in my name only because I was able to take time away from work to close, just for example. If something happens to me, it will go to him without probate, even if I didn't have a will (which I do).
Also, our vehicles are in various names, depending on who could get to the courthouse at the time of purchase. Ironically, I think he owns my daily driver, but I own a large truck and a trailer that I cannot easily drive (not at all in combination and the truck alone with difficulty and a pillow behind my back).