Think about the fact that you and she both needed a few alcoholic drinks in order to handle things. That is a red flag, and indicates you are both not ready for poly yet. You should be able to act in a clear-headed state and face the truth of a situation in the moment, and to be able to make choices without booze clouding your judgment.
You do realize that most couples take a year or more to get from the stage of thinking about polyamory to actually doing anything like having an additional sexual partner. Why are you in such a hurry?
Hot chick in the city.