Just my two cents...
I hate to break it to you, dude, but once you have to start setting rules for your partner, you might as well just move on and find somebody that you can actually trust. She clearly wants outside of the boundaries you want to set for her, so my guess is that if you take her back, she's either going to leave you after she gets over the initial guilt of this incident ("I want to fuck other people and I know that hurts your feelings so bye"), or she'll decide she really doesn't give a fuck and do it again ("I want to fuck other people so I did, bye"). Either way, I doubt she's going to find the relationship fun anymore even if you somehow manage to avoid bombarding her with bad vibes of distrust and guilt, so if I were you, I'd just pack my shit and move on to bigger and better things; don't make a scene, don't get anybody else involved, don't lose your shit or get depressed, just go and rebuild. You're full of shitty feelings, I know, but they can be channeled into something constructive; one of the best things you can do after ending a relationship on bad terms is to go out and do everything in your power to make yourself into a better person, even if you're only doing it for the spiteful hope that you'll come across them again someday and they'll have no choice but to hate themselves for leaving.
Leaving now (which, in case you missed it, is something that I strongly recommend) is going to hurt like hell and leave you with a lot of "what if"s, but leaving a month from now after desperately trying to keep a relationship pieced together because you're afraid of letting go of someone that once made you happy? That's like refusing to stop playing Russian Roulette after the fifth click. I know you're telling yourself that there's always a chance that things will work out, that your circumstances are special and the only reason that there are naysayers is because you must have left out some crucial detail that would otherwise change their minds, but... well... I don't know what else really needs to be said. If you insist on trying to be happy with a Frankenstein relationship ('cause you're reanimating a corpse, geddit?), at the very least, you can take comfort in the fact that you'll definitely learn a strong lesson from it, and probably grow up quite a bit, as well.
EDIT: P.S., that talk you want to have with her tomorrow? If you go into it hoping that she's going to promise you a perfect happily-ever-after where she feels so shitty about what she did that she can't be anything but the most wonderful spouse ever, the end result is going to be whatever she wants. Please, dude, if you're going to volunteer to leave yourself open to that, at least have enough sense to take time to yourself to decide for sure just how you feel about this, and whether you want to take the chance of continuing your relationship. Miracles are not summoned by way of patient suffering.
