If your girlfriend's sister has an L cup, is crazy about you, and begs you to have sex with her, can you resist?

When I went to her house for the first time, "Ui", who fell in love with me at first sight, was already aiming for me. "It's a secret from your sister, okay?" Ui, who knows that her big breasts are a weapon, goes braless and presses herself against me, trying to destroy my dick and my reason. Even though I know it's no good... even though my girlfriend is right next to me... I ejaculated over and over again with Ui's soft breasts... Ah, I'm the worst...