It's "funny" how kouhai change camp just the next day, circonstance on cheating? That doesn't exist.
I can totally understand if the ex felt left alone (while MC just had problems with his club ...) and felt insecure about Ayaka, that's understandable but that's an excuse to have a good chat, no directly hold hands with another guy in front of his house. At the beginning i thought maybe she just "tried" the old and stupid game of doing that to make him chase after her more, tho it backlashed into him breaking up.
But no, she just admitted herself to cheating. And bro got forced to 2nd guess by both Ayaka and Kouhai? While i think Ayaka's point is valid here in the way she said it, since she's not close at all with Reina and don't even know her personnally she can only side with her best friend. So what she said isn't wrong in that sense.
But Kouhai? Shouldn't she be even more protective of her dear senpai ? Instead she gaslight him? Maybe it's her way to let him go and hear the "whole" story for him to really have a closure since he doesn't seem to be able to do it without it but it's badly done :/ Here for someone already doubting himself wether he did something wrong or whatever it's just like she's siding against him.
Does she want to send him to Ayaka that much ? I wonder what Ayaka really did in the past for all those girls to hate her that much.. Apart from that i'm not really sure Ayaka love MC, sure there is no doubt that he's an extremely special and important existence for her but does she love him as a BF, future hubby? Not sure
As for MC, he seemed to have comptely erased any developping feeling for Ayaka and really see her as his best friend, someone important, but not a lover. (Though i can understand why other girls interrested romantically in MC might be suspicious/jealous of her, on MC's side there is really no reasons for that)