If you enjoy riding together, start saving/looking for a tandem. Makes it even more fun. You can pull a trailer, too.
By the way, Trek calls that style frame a Lowstep. A mixte frame has two parellel stays running from the headtube to the rear fork ends (according to Sheldon Brown).
Not sure why Trek thinks the Ladies' style frame isn't obsolete, but there seems to be a market for it.