Woman Please Help! How should i initiate a negative convo with my Girlfriend?

I think you have every right to feel the way you do and if anything, she is very lucky to have as understanding a boyfriend as you are to even put the time and effort into wanting her to know how you feel! In my opinion, she is a little in the wrong for making it clear that you are not welcome. However, her newfound social life is probably more of her outlet to feel like she has a life outside of her relationship with you. Most girls (and I'm one of them) don't like the idea of being known as "so-and-so's girlfriend" and strive very hard for people to see them as more than that. This trip that excludes you is probably not out of malice, but because she is trying to carve herself an identity. Just explain to her your concerns as calmly as your question just was and she'll understand and appreciate your honesty!