Yeah I'm on your girlfriends side in this. Does she have to tell you every time she goes anywhere with a guy??? Where's the trust in this relationship?! Besides its not like she went off with some guy all day, there was a big group of girls there too, it's not like anything would ever have happened anyway. So maybe he DID call and ask if he could come along (you know some girls do actually have male friends, y'know - besides even if he WAS interested in one of the girls there 1. it might not be your gf and 2. you should trust her enough to say 'no' if someone else was ever interested) in which case when was she supposed to tell you?! Its not like she needs your permission to go somewhere with a male other than you. I'm in a LDR myself and you have to trust your partner otherwise this wont last.
"When I was 4 years old, they tried to test my IQ.
They showed me this picture of 3 oranges and a
pear. They asked me which one was different and
did not belong. They taught me different was
wrong."
- Ani DiFranco -