Now that we got a clear version of Chapter 29, it’s obvious that Reina cheated on Yuuta because of her insecurities. When she talks to Mayu, she asks, “Hey Mayu, where do you think cheating actually begins?” Mayu replies, “Isn’t it the moment you start asking that question?” Reina then says, “I see. Then that means I cheated on Yuuta, and he didn’t cheat on me.”
Mayu follows up with, “I think cheating is the worst. What about you, Reina-san?” Reina responds, “I think so too… but I also think sometimes there are understandable reasons for cheating.” That line right there tells me Reina cheated out of insecurity.
And I guarantee whatever she’s about to confess to Mayu has something to do with Yuuta’s close relationship—or even just his friendship—with Ayaka. They’re extremely close. And earlier in the chapter, Mayu admits she’s a bit insecure about Yuuta’s bond with Ayaka too. That’s why she asked him if he had romantic feelings for Ayaka, which he denied—but he did say he cares about her deeply. That’s his best friend, someone he’s known since high school, so of course he’d care.
Reina probably saw that same connection and thought the worst. If that’s the case, it might explain why she ended up forming an emotional connection with the pageant organizer—why she was holding his hand. That’s still cheating. Emotional affairs count. If you’re emotionally invested in someone else in a romantic way, and they’re not your partner, that’s cheating.
So in the end, it doesn’t change my original stance—Reina was dead wrong for what she did. What’s strange, though, is that she says she wants to “start over from the negative.” She doesn’t want to give up on Yuuta. I think that’s part of why Natsuki, her best friend, is pressing Yuuta so hard. She probably sees the connection he has not just with Ayaka, but with Mayu too, and wonders why Reina is still trying so hard to get back with him.
That’s just my opinion. I mean, I could be wrong—but I don’t see any other reason Reina would say, “I want to start over from the negative,” unless she genuinely wanted to fix things and get back together.
Still, if she cheated because of insecurity, that’s a huge red flag. That kind of person will do it again. And no one should have to be emotionally invested in someone who might let insecurity drive them to cheat. Just my two cents.