Not So Innocent GF

My gf (16) always likes to act innocent around her family but whenever we are alone she surprises me with how horny and sexy she gets. She’s obsessed with my big balls and loves it when they smack her chin and bounce on her clit. We had a sleep over and I thought she was going to get mad at me for making too much noise but she actually pulled my hands and told me to keep fucking her. She was trying her best to not moan but her pussy was making a lot of wet noises and we woke up her big sister.