Ms. Davies is heartbroken, unable to comprehend how Terry could betray her trust like this and simply offer her up to his best friend as if she were some object. She thought what they had was real- not just some fling that meant nothing. Before long, she quickly realizes how stupid she was to even start something like this with Terry. After all, he's just some high school teen with barely a scrap of life experience.
Ms. Davies outright refuses to go along with Terry's plan... which is exactly when Paul steps in to take control of the conversation. He's not as much of a pushover as Terry is and has far less of a moral code. Paul manipulates the situation, convincing Ms. Davies to give him a blowjob, and then eventually the rest of her body. He even lets Terry step in to DP her, allowing him to join in on the fun. It's clear that after this, however, their friendship will forever be changed.