Well, we said "'Til death do us part" until we realized that death doesn't have to separate two people who long to spend eternity together. Indeed, the funeral industry is able to provide mostly lovely, always fascinating ways to keep love alive. I've known elderly lovebirds who've retained the cremated remains of the partner who died first, requesting that all ashes get co-mingled when the inevitable eventually occurs. Other families are better pleased by placing Mom's and Dad's remains in a large urn sized for couples that has two tidy, separate compartments.
This can be a powerful statement from couples who've worked hard to keep their ardor and commitment alive, and want to stay together forever. (Reminder: nearly all cemeteries accept "companion" cremation urns for burial or niche placement just as they have always buried deceased married couples beside each other. Just let the staff know the urn's dimensions.)
If you're holding the cremated remains of your dearly departed parents on a hall closet shelf, you might consider buying something this Valentine's Day or on their anniversary that could sweetly house them together. Also, a plaque on a park bench is a splendid way to honor them, or an actual bench for two in the cemetery beside their graves would be an incredibly generous gesture.
Of marriage and coupledom, the poet Robert Frost once wrote, "Two such as you with such a master speed, cannot be parted nor be swept away from one another once you are agreed, that life is only life forevermore, together wing to wing and oar to oar." And apparently, that summed committed romantic relationship up so well for him that he used that last line under his wife's name on their shared grave stone.