Ethan 2 goes from being the perfect guy to a selfish cheater (E2 becomes E1). Sophie 2 goes from the happy and kind version to angry and hateful and loses the smile (S2 becomes S1) Ethan 1 gains the ability to admit fault and promises to be a better man (E1 becomes E2) Sophie 1, upon seeing the change in Ethan 1, loses the frown and gains the smile and happiness (S1 becomes S2)
So at the end, S1 gives Ethan the same smile and nod she gives him in the bathroom after he admitted his fault (S1's "tell" at the end is the smile and nod, the same tell that S2 had in the beginning).
In effect, S1 and E1 become the better versions of themselves. They both leave acting like E2 and S2. So you could say that S1 and E1 gave up their bad versions which were left at the house. The house served it's purpose, it forced them to change.
You are correct, sir. I don't have anything to add but just wanted to get this to the head of the comments so future people coming here with questions will get the straight dope right off.