Ask any questions about the dilemma and I will give a thorough answer to aid your decision making process.
What makes you think a bunch of randoms on a poker forum, with a demograph heavily slanted toward guys who will respond favorably to your position, gives you more insight into the situation than your girlfriend? Relationships are supposed to be based largely on open communication and if this is a gray area where she isn't comfortable, you should consider that.

There is a 0% chance that you hook up with one of the girls at the party. You have discipline. Even though they might be getting super drunk, horny, and flirty.
I was trying to come up with a smiley face that would convey the following: I trust based on how you are asking that you are sincere that you don't want to cheat on your gf, but a) you don't understand the mathematical implications of 0% (super nitty) and b) from a practical standpoint I'm sure you know there is a non-trivial chance that you are hooking up with some rando there even if you don't intend on it.