I've said I don't think Christians have a duty to bury their dead. I think the choice between burial and cremation is adiaphorous. Cemeteries are of value to the living, not the dead. If survivors visit the cemetery, then burial is beneficial. But after a generation or two, the grave will be neglected and forgotten.
Traditionally, married couples used to buy companion plots. These were two burial plots side-by-side. Typically, one spouse predeceased the other (unless both happened to die in an accident or plague), and was buried first. The surviving spouse would be buried beside their spouse. The tombstone already had a birthdate, while the date of death would be filled in when the time came.
I think that arrangement is commendable–for couples who can afford it. Admittedly, this is all about symbolism, but the symbolism is potent. It sends a message about an outlook on life that may be alien to many people with a post-Christian worldview.
Just in general, cemeteries make death a public fact. They don't conceal death. Cemeteries are a visible and enduring reminder of our inevitable mortality. That's something many people avoid thinking about.
In addition, companion plots symbolize ultimate devotion. Where you marry someone with the intention of remaining together for the rest of your life. And even in death, a companion plot is a token of their inseparable bond. Love that's stronger than death (Canticles 8:6).
Again, it's just an emblem of their devotion. Only God can actually reunite the dead. But it's a powerful witness to the world.
Marriage is sacrificial. Due to our mortality, and the brevity of life, we can only make our life with one person at a time, and we only have one life. Life is a card we can only play once. That deck will not be reshuffled.
Marriage opens up many opportunities within the bonds of matrimony, but by the same token, it forecloses many other opportunities. To make your life with one person, to have children by one person, is to foreclose the opportunity to make your life with someone else, or have children by someone else.
Even if, due to divorce or premature widowhood, you remarry, you can't really start over again, because you can't make up for the lost years. That's time you will never get back. The hourglass only has so many grains of sand. Time is running out.
There are forks in the road of life where you must choose to go right or left. You can't do both. Whichever road you take you must take all the way to the end. By going down one road, you deny yourself the chance to explore other roads. That makes certain choices momentous. You give up a lot in the hopes of getting a lot in return. It's a gamble. You bet everything on that particular relationship–for better or worse.