Love exist as well as hatred.
Someone just being exist can give birth to these emotion because this kind of thing.
Well, fujishiro is aiming for manabu because neither manabu nor amano tried to do shit about their relationship, so its still fair game.
And the last dude, just go chase some other chick, how unhealthy can you be to chasing skirt while copying everything she does?
Good thing this isn't some hentai doujinshi, otherwise, his end wont be pretty