He was not even thinking about yuki to begin with until they played his song he was worried about his and uenoyama's relationship and music and totally haunted by his past trauma, his ex boyfriend killed him self over a stupid fight which he believes is his fault, thing like that you just can't shake till you die to be honest IT IS A BIG DEAL. Which was not even his fault because yuki always has suicidal tendencies his mother also mentioned he was just like father ( who took his own life just like he did) she also said to mafuyu that he was like a anchor for yuki to hold on to this world, yuki portrait a dominant character and put on wall upfront and created a super perfect personality but he was suffering from self conscious and self doubts , at beach he said "I am sure you gonna forget about this day" and the more he talked felt like he was not seeing mafuyu in future (self doubt) thou mafuyu was everything for him he never wanted mafuyu to see that side of his that's why he never asked mafuyu to join the band, he created a boundary around him and pushed him away he knew mafuyu's love for music but still he left him behind, he wanted to write a song for mafuyu in all his own but all mafuyu wanted him to understand that he wanted to do it with him, due to his parental trauma mafuyu never had courage to keep his thoughts up front and he still struggles as he mentioned " my dad hits me when I speak" that's a lot man, childhood trauma is no joke, yuki pushed him to the point that he stopped seeing him that made mafuyu angry(of course) yuki said I can't live without you in reply he said "so are you gonna die for me then? It was normal couple fight but for yuki it was more like a permission due to his suicidal tendencies SAD!! but toxic yuki kept him in a box and mafuyu never realised it because of his introvert nature on the other hand