I succumbed to the temptation of my girlfriend's older sister's braless breasts and had sex over and over again.

I've been dating a girlfriend who isn't beautiful but has a good personality for half a year. When I go to her house for the first time, I am introduced to her older sister. Her older sister is extremely beautiful and has an excellent figure, and has H-cup breasts, and for some reason, she doesn't wear a bra and my eyes are glued to her breasts, which seem to be spilling out of her clothes. Later on, when I went to my girlfriend's house to pick up something I had left behind, I found myself alone with her older sister, again without a bra, and the older sister was holding her breasts close to each other.I tried to hold back, but I had reached my limit and my crotch was fully erect. I ended up doing it.