Ya, I understand that might be more realistic, but personally I think stories like this one benefit from drawing things out a bit more. Keep finding creative ways to put the main characters into situations that present temptations that push them further than they would go otherwise.
To me, and this is just my opinion, once the main characters go all the way, the story usually goes stale and is in danger of becoming like a hundred others you can find out there. At that point, either the game is over for me, or the storyteller needs to give me something new to work towards, like drawing one of the other characters into their relationship.
So, again just my opinion, I hope the creator of this game continues to push things forward in a natural way and doesn't rush to the finish line prematurely.