My Secret Affection, Volume 1 (My Secret Affection #1-4)

Ever since the day thirty years ago when a strange meteorite crashed to earth, heterosexuality disappeared. Life changed drastically, and the world embraced same-sex relationships. After Kazusa Takanashi is dumped by her girlfriend, she's astonished to find that the new object of her affection is her childhood friend, Ayumu. But... he's a boy! And not only that, his grandfather was in space the day the meteorite hit, which made him the world's last heterosexual. How can Kazusa navigate these newfound feelings if no one else around her feels the same?