You hear your stepsis got a call while she going to the bathroom. Apparently she needed to pee when her boyfriend call her. She forgot about her need to pee when her boyfriend started teasing her. I can see how she gets turned on through the gap on the door. She starts touching herself and talking dirty to her boyfriend. You can help it and start jerking for your stepsister. She can't see you. When she cum, she can't hold her pee anymore and makes a big mess. That's when she sees you jerking to her. But she is as ashamed as you are, so nobody gonna say anything. This is a secret between you two now.
