My beloved stepsister, whom I raised, was slept with by my worst friend… Jinguji Nao JUL-920

Jinguji Nao isn't my real older sister; she's my stepsister, brought along by my father's remarriage 10 years ago. My parents passed away a year after their remarriage, and I was raised by my stepsister, whom I also admired. However, she was actually slept with by my worst friend, Yuzuru…