Is this behavior acceptable in a relationship?

[AsH_KeTcHuM]

I'm in a LTR with my girlfriend going on 3 years. I have only a couple of very close friends that I breakdance with, and workout with. But I recently joined a hip-hop dance team called Culture Shock and have a lot of new acquaintances. Its a co-ed team, all around my age, and of course we are all dance enthusiasts, so I seem to get along with them pretty well so far despite my introvertedness.

Anyways, the first team party was a couple of months ago, and I wanted to go on my own without my GF. She was offended by me wanting to go on my own and we had a big fight about it. I then said I'd take her, but Another fight we got into led to me saying "f-it Im going on my own now." Which I did.

I didn't hook up with any chicks there, and to be honest there's only one really hot chick out of the bunch, so it was a pretty harmless night.

Another one is coming up, and again I just want to go on my own. My G/f is upset again, and thinks I want to be all touchy feely flirty with the girls and thats why I don't want her going. She says she cant trust me, or them, when were all drunk and stuff.

To be honest I don't know exactly why I don't want her going. I guess because I like to act differently around my boys. Also I tend to act like a jackass when Im drunk, my girlfriend gets pissy and kills my buzz also. Theres noone there I'm trying to hook up with, and although I would act differently when my girl isn't there, I'm not planning on doing anything definitively bad.

I understand why she would be upset that I'm not inviting her to come, but I don't know whether its reasonable of me to expect her to accept my wishes or not. Do you guys think its ok to separate your s/o and social life like this? Also I don't party or club a lot if that makes any difference.