Today is the first time I visited my girlfriend's house. That night, while we were making love, her sister suddenly opened the door and saw us in the act. I felt extremely embarrassed and was about to go apologize to her. As I approached the door, I was mesmerized by her beautiful huge breasts as she was changing clothes! The next morning, while my girlfriend was doing her makeup and changing clothes, her sister kept using her large round breasts to seduce me, causing my manhood to quickly swell. Despite liking my girlfriend a lot, her sister was too seductive! "You don't need to wear a condom when making love to me," "You can ejaculate a lot of sperm inside me." She continuously seduced me with things I couldn't do with my girlfriend. The thrill of secretly ejaculating into your girlfriend's sister's vagina made me extremely excited. Even when my girlfriend unexpectedly returned and discovered us, I couldn't stop making love to her sister. In the end, I ejaculated inside her sister's vagina in front of my girlfriend!