Back when my wife was physically able to ride we rode both Tandems and single bikes.
On the single bikes I would ride at her pace and we both enjoyed the opportunity to ride and explore our little corner of the world together.
On the Tandems...I was the Captain and she was the Stoker and that was the way she liked it. The pace was gentle and again we both enjoyed it immensely. Passers-by often asked "Who's working harder?" and we always instinctively pointed to each other.
Prior to her 1991 diagnosis we always rode single bikes and she rode like the wind and I worked hard to keep up with her, but those days are a distant memory now.
I dream of getting her back on the EZ Tandem for short four or five mile jaunts but it will probably never happen due to the M.S.
To all of you who are able bodied couples I implore you to just ride together as much as you can. You never know when it will all be history.