I also think that the therapist may not be the way to go to start this couple on their way to swinging. I do like the idea of being able to control both the husband and wife but it may be a good idea to make the switch between the two optional. Part of the appeal of this game would be wondering what the other partner is doing when you're not around so you may not want to give too much away Instead leave clues as to what happened that the other partner can find. You could have a mechanic whereby both the husband and wife go on dates at the same time and you have to choose which one you will play on the date. Then when you are on your date the computer is selecting options that the player would have gotten to select if they chose to be that character. What your partner does on their date would then be based on choices you made before that point (if they're mad at you they may go further on the date than you both agreed for example).

*laughs*
Okay what kind of story do you want...
a tame story
a tempting story or a story that's hmmmm...
or is it a story that you yell? "Put it back in the box put it back in the BOX!"