The young man married his younger sister but likes to fuck his older sister

I and my girlfriend are preparing for marriage. Today I visited her house and met her older sister, Riho-san. I've seen her photos before, thanks to Kurumi, and I knew she's the idol I've admired for so long! She's even more beautiful and charming in person! She seemed to be inviting me too. She let me admire her beautiful breasts, blew me, and most importantly, allowed me to have sex with her without a condom! Even though I'm about to get married, my girlfriend still insists on using protection, so being invited by Riho-san like that made it impossible for me to stop! Our secret relationship continues like this until the wedding day. She and I plan to have sex one last time and end this relationship.

But unexpectedly, Kurumi found out. Despite being discovered, we didn't stop. I ejaculated a lot of sperm into Riho in front of Kurumi. I'm not sure how the wedding will turn out, but I know my bride won't be Kurumi anymore, but her beautiful older sister...