A lot has happened in the short time you have been together... monogamous, cheating, poly, monogamy again and now poly again... that is a lot of roller coaster rides. I think you are being impatient.
You cheated on her, I would think there is a certain amount of trust issues there that would make this process longer than perhaps it would of been for starters. Secondly, she might of played at poly because your relationship with her wasn't that stable at the time and meh, why not get affection elsewhere? Thirdly, it sounds to me like she is monogamous and thinks that in order to keep you she needs to be a super star girlfriend and learn to be okay with your dates (the sex the night before etc makes me wonder about that).
My experience with mono/poly dynamics is there is never a boundary that is nicely placed and feels good for all.... I am always compromising and so is Mono. We have just learned to feel uncomfortable sometimes and that it is what it is. Neither of us have been able to figure the other out around the issue of me needing more closeness and connection to others in the form of sex so that is where my relationships stop growing. I haven't been able to understand that he doesn't get that it has nothing to do with my love for him.
On this note, maybe you need to realize that you might never get to a place where you feel entirely free to walk out the door without a struggle and she needs to realize that she might never reach the place where she feel comfortable with you going off to date other women. It might just be that you have to both live in that and see it for what it is. We don't always get our way in life, but if you can get close to it, then that is the best you can do.... that's been my experience anyway.
You might want to do a search in the tags for "mono/poly." There is a lot here on that topic that might help... "cheating" might help also.
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