
Such a childish reason ...

I'm pretty sure the real reason Yuki broke up with him was to protect Atsuto's career as an idol. The first page it shows atsuto's debut and Yuki watching, it also says "someone's crying" "only a select few can stand on this stage". Them being in a gay relationship would have destroyed Atsutos career as an idol if they were ever discovered (which it probably would, paparazzi/fans are cray) so Yuki cut it off with an excuse like "we rivals so bye" but for the sake of his love for Atsuto. Just a theory
So it’s not sum supernatural?? It’s just his mind? I am to dumb to get this I see
Don't worry. It's his mind, yeah. It's named disociation, it happens when our minds have to cope up with trauma, a extreme case of distanciation between our emotions and our concious. The cold robotic Ken has cancel the emotional raw Ken and took decisions for him and now he is awaking because of Yutaka and began to take irracional decissions and having flashbacks of the past.