so basically he sorta changed her from him being so nice, and charming. Then after it all her dark tendencies were still there but instead of taking it out on others specifically, it was aimed at others for the sake of him or such. Maybe because of that he started to back away when it got too much and over the top, in which it got worse and the rumor of him being mean to a girl or such and the life ending incident put him over the edge. Theory but it is seeming that getting involved with a type of Yandere girl who did not care for him at first until he charmed her... Took a toll on him. His charm was still there the entire time, but with how weird he was due to the incident, and also being an otaku, he just flimsily kinda thought he was a loner and distancing himself from others until the heram of girls countered his way of thinking. XD