BF-688 Sneaking around with your best friend's girlfriend

Today I gathered at my best friend's house and drank with my best friend and my best friend's girlfriend, Jun-chan. It was late at night so I decided to stay the night. When I was about to go to bed after drinking a lot, my best friend and Jun-chan started flirting with me. Wow... I thought that was crazy... but my best friend fell asleep. Jun, who was disappointed, noticed that I was awake.