This is the kind of plot if Akutsu were actually a bi***. She clearly likes him and he likes her they haven't messed up their relationship at all it is just a slow romance with fluffy moments. If she were actively hurting him or talking to some other guy or even just ignoring him then the development described would work. I am all for stories where the MC finds a better girl than the one he initially simped for however that is not what is going on. This was two people who were different from one another coming to like each other by spending time together and appreciating each other's company.