My girlfriend's older sister doesn't like wearing a bra

I'm dating my childhood best friend's younger sister. One day I went to my girlfriend's house while my sister Koyoi Konan was at home. She was beautiful and without a bra she wanted to cling to me. It seems like Konan is jealous of her younger sister and wants to steal me. It's true that her sexiness makes me unable to control it. My cock kept getting hard every time I looked at Konan's exposed nipples and the discomfort gradually increased. And then Konan and I secretly had sex behind my girlfriend's back in her bedroom.