My girl best friend (23F) has been my best friend since we were children - she's been in my life since forever, and I would NEVER think of dating her. We haven't seen each other in forever as we live on opposite sides of the country, so when we learned that we happened to be nearby in the same place for the first time in years, we were elated. Because of this, we've been planning to hang out on and go on trips to nearby places around the area just for fun, as we haven't gotten the chance to hang out and have fun for a long time. I'm going on this trip on a work trip, so my girlfriend won't be coming with me, while my best friend just happens to be there for her studies.
However, while I really want to hang out with my best friend, I want to make sure to be sensitive and not upset my girlfriend. I can see why it would be upsetting - my best friend is apparently quite conventionally attractive as well as very smart and accomplished, and she's straight, single, and my girlfriend knows that we're very close. So, I was wondering, is there really a way to go about this properly? How do I tell my girlfriend? Is there even a chance that I can go on this trip without fucking up my relationship?