Tim and Robyn had been dating long enough to know that the next step was to move in together. Of course, this made sense since it meant that they could now consolidate their lives, cutting down on several living expenses and also spending more time together. But this had nothing to do with romantic quality time, which is how they filled the couple of hours they had alone on weekends up until that point.
It is true that you need to live with a person to truly know them, and once the two had moved in together, it was a matter of hours before they realized just how deeply they could now explore one another. And to both their surprises, it turned out that the rather conservative pair had inner animals that they could now bring out to play, given that they had all the time in the world and every room in the new apartment was now their playground.