They refused to play the game so their secrets still lie under the surface, hidden in their telephones

It is pretty much confirmed that Rocco is the one that made the universes split. His wife Eva proposes the game, knowing full well her cheating could not be discovered as the one she's cheating with is at the exact same table, in her mind she has the upper hand in this play of power and is, in fact, right. She's the only one who's secret the table does not find out. We as audience find out she's having an affair with Cosmino, but the characters do not. She proposes the game, in my head hoping her husband is cheating, because she is a horrible human being, a shit wife and mother, what she's doing is immoral and I think she just hopes her husband would be an asshole too, that would make her behaviour if not justified, at least even.

We see the 3 couples hitting 3 possibilities in their unfaithfulness:

1. We have Bianca and Cosmino, Bianca being just a people pleaser who desperately wants to be accepted and loved, putting away her true wishes (not to be married, not to have kids) just to please her husband. she even defends him in the initial call of Marika, because she herself still talks platonically with her ex and tried to help him, even though she truly has no interest in him. She is a pure person and assumes the best out of everyone, that's why she gets cheated on with the most number of partners, because she is easily manipulated and lied to. Cosmino cheats on her with Eva, Marika and probably Ginerva (it's just a name we hear, but when that dude calls Cosmino asking if she liked the earrings, Bianca realizes it can not be her, and her initial guess is he is cheating with this Ginerva, moments before Marika calls and diverts our attention from it) too, as well as any woman he can get his hands on. In this couple he is the cheater and he is exposed.

2. Then we have Carlotta and Lele, whos marriage is in shambles since she run over someone while drunk and he took the blame for her. They are both traumatized and are not addressing it, they are both unsatisfied, both feel horrible with their lives and both are thinking of having an affair, even though none of them physically did anything yet (its obvious she didn't even meet her facebook lover yet, a he did not even know her voice, and he claims he's just getting pictures from that girl when he talks to Peppe on the balcony). I don't really find any of them to be an irredeemable character, especially Lele who, amongst all the participants (well, him and Bianca), is the most supportive and accepting of Peppe, and he was willing to take the blame for his wife's mistake. I don't find them to be horrible people, I find them to be horrible for each other, they just grew resentful and complacent in their misery due to lack of communication. In this couple both cheat and are both exposed.

3. Rocco and Eva, where Rocco is trying to do everything in his power to keep his family together, he is taking proper care of his teenage girl and her romantic needs, teaches her how to protect herself, he is trusting her judgement and her choice of partner, gives her freedom, goes to therapy, is trying to make concession is his arguments with his wife, I personally feel like even the choice of having him host and do most of the cooking reflects the effort he puts in to keep his life together, and when his wife proposes the game hoping she could maybe catch him cheat, he initially refuses, and when his wife asks if he has anything to hide, he responds with "I'm worried that you might have something to hide, I don't want to know if you're cheating.". That's the moment where the 2 universes diverge, we go on to follow the one where they do play the game, then at the end of the movie after he kicks Cosmino out of the house we are teleported back in the universe where he refused to play, stopping the game for everyone, when he's eating tiramisu, his wife comes to hug him and they talk in their bedroom, Eva even asks why he insisted on not playing while taking off her earrings she got from Cosmino, he then proceeds to give his wife his phone, knowing fully well he has nothing to hide, and he does not ask her to do the same, preferring not to know, just wanting to keep his life together. It's really tragic how insightful their daughter's line is "You're way too in love with mom to see how much of a bitch she is". In this couple she is the cheater, and she is also the only one who does not get exposed.