@VirginWaifuFTW The entire point of this manga is that both grown to love each other more than their crushes, but both couldn't just give them up.
Akari never thought about Jirou as her back-up or a main choice, just because she tried to keep her sights on Tenjin, despite falling in love with Jirou. Tenjin shooting her down was a lucky thing for her for the very same reason and manga specifically noted that what she felt there is not heartbreak, but relief.
Same thing with Jirou. He doesn't care about Shiori just as much anymore, even if he tries to convince himself that he does. Shiori kissing him out of the blue brought him only more distress.
Also, honestly, she deserves to lose due to unwittingly friendzoning Jirou when he was about to confess to her. Even if she always had her arrows set straight at him.