My whole thesis with this unique yet absurd/genius premise is that Yuu-kun don't even have the right to be upset or feel betrayed at this point. Normally the setting would be she loved you and there was a genuine commitment and you sacrifice and put in everything for the relationship only for her to throw it all away to get dicked by a guy she just met, that's understandably heartbreaking.
Here the script is flipped where she meticulously planned this whole thing out before she even stepped into the daycare and selected you. Put in a whole 10 year timetable of work (like scouting the water park and organise the excursion to work in a bra slip opportunity) all for the sake of ONE moment of eventual "betrayal" that ultimately amounts to "sorry I like someone else" during high school or some shit.
Meanwhile Yuu-kun remains your awful wish fulfilment harem MC who does nothing yet all the FMCs fall for him. Hell at this point Yuu-kun is the clear villain if he DOESN'T give a satisfying reaction after all the work she put in. Like he could literally just respond with: "oh alright, that sucks" and I will be like "ya that's a fair reponse since you put in nothing, but just know despite how illogical it may seem, you're in fact the bad guy."