My Childhood Friend Who is My Girlfriend was Stolen by My Best Friend. From Now on, I’ll Flirt with My Ex-Best Friend’s Little Sister!

It’s only been three weeks since we started dating. And yet, I was cheated on. To make matters worse, the one she cheated with was my best friend. When I finally gathered my courage to kiss her, she told me that it was ‘too soon’. However, she just kissed him without a hint of hesitation. Betrayed by the girl I’ve loved for so long, my childhood friend, and by my best friend, I was heartbroken. At that moment, my best friend’s little sister appeared. She held my hand as I was feeling down and said, “I’ll become your cheating partner, Senpai♡ Let’s teach them the pain of being betrayed.” Thus, my revenge began──! However, as I spent more time with her, my lingering feelings for my c...