A lotta people confuse the idea of being in love with someone with actually being in love with them.
the two are very different and I can honestly say I've only been the first and figure one of these days I'll truly be in love with someone, but whatever, that's irrelevant.
Tell her the truth and understand that you're never going to have the same relationship with this girl ever again, ever since that night the nature of your relationship with her has forever been altered.
It's inevitable that she's gonna find out, and when she does if she decides to give you a second chance, she's not going to look at you the same way again, she'll always be doubting you. Until she finds out you're always gonna be nervous and wondering if she knows already and you're gonna be nervous cuz it's gonna be at the back of your mind until you eventually tell her or she confronts you.
Think of it in those terms and the solution should be obvious.
You don't need the drama, just tell her straight up and let the chips fall where they may.
If she gives u a second chance and if you really wanna stay with her and hope that one of these days your relationship can evolve into something truly beautiful than go for it, but understand you will never again be where you are right now with this girl.
Learn from your mistakes and move on, and heaven forbid don't ask for personal help here.
"Dinner is just a meal until shared with family, as Love is just a thought until shared with others."