The Mortal Enemy Is My Student

In order to pay for college living expenses, I took a job as an English tutor. Only when I arrived at the student's home did I realize that the person I wanted to teach was my archrival for three years in high school. He didn't know it was me who was here, and I didn't know it was him who was going to teach, but his dad didn't even know that neither of us liked the other, so our first tacit understanding was when we pretended to be strangers in front of his dad.