Fucking My Little Sisters Best Friend For Years

A bit of a complicated situation and someone suggested I post about it on Reddit to see what people say.

I’m about 26 male and been hooking up with my little sisters best friend (21 F) for yeaaaars now. My sister has always been friends with her, and I’ve known her forever. When we started hooking up a number of years ago now, we knew my sister would be insanely pissed about us hooking up and we said we wouldn’t ever do it more than once.

Well it’s been a long time now and we are still secretly fucking. She has a boyfriend and I have a fiancé. It’s one of those situations where I truly have never thought of what we do as cheating. I’ve been meeting her and hooking up for a long time, and known her forever in a non romantic way. Every gf I’ve had the last few years, I’ve still been seeing her in secret.

Well I went out to visit my sister and her friend at their college campus for a weekend. Her friend and I kept sneaking off away from my sister, and her besties boyfriend. We genuinely had the hottest fucking sex while sneaking around this time.

We fucked in the bathroom of a college bar, we snuck off to a hidden room at a house party, and unfortunately got caught fucking by my sister.

My sister was LIVID and fucking lost it. She lives with her best friend, and we were fucking in their apartment when she walked in on us. My pants around my ankles, her on top of me moaning at the loudest volume possible. We lied and said it had only just happened this once. My sister said if we hook up again she will tell both our significant others. She’s PISSED.

Wrong to keep fucking behind her back but keep it on the DL?