They start having sex. And you watch.
You tell yourself you're about to go. Any second now. You just need a moment to process what you're seeing, and then you'll quietly close the door and walk away and this will never have happened.
That moment stretches. And stretches.
At some point you become aware of your own hand. It has unbuttoned your jeans without any conscious instruction from you. Your cock is out. Your body has apparently decided that after everything happened today, it has had enough of waiting. It wants to cum and it wants it now.
You watch Charlotte. Your hand moves. After weeks of accumulated desperation your body is running entirely on its own now, chasing that orgasm with the single-minded focus of something that has been denied too long.
You are almost there.