Should I Tell My Fiance I Popped Her Sister?

Me and my girl are madly in love and engaged to be married, but some years back before we got together I popped her sister. This went down about 2 years before me and my fiance hooked up and we've been together for 5 years. She never knew me and her sister had sex because it was like a one night thing and her sister never mentioned it to her. I don't wanna lose my fiance, but I do feel kinda guilty about keeping it from her. Should I just leave the past in the past or should I tell her?

SpeekDaTroof: Keeping it real, if you wanna keep your fiance and don't wanna end up cancelling your wedding, leave the past in the past. If I'm doing the math right, that sh*t happened one time seven years ago. Just leave it in the past.