Echoing most all of the comments above, we've had our T1000 for a year now and ~3000 miles later we both agree it's the 'second' most fun thing we do together!! Wish we had gotten it years ago. I can't think of anything better for our health and overall relationship --although I can see if the relationship is rocky, the tandem might not be the best first step!
We occasionally ride singles but like everyone has mentioned, it's mostly 'at the same time, not together'. But you two sound ripe for one! Go for it.
Let us know the results.