When To Pass Up a Free Vacation

I recently found out that a group of friends of a good friend of mine is going to the Outer Banks in early September, and they invited me to go. My friend can't go, and I desperately need a vacation and want to go. However, while I really like these people, I just don't know if I would feel comfortable going without her. I think deep down she would be somewhat jealous if I went with "her" friends, plus one of the guys in the group is totally cute and if something were to happen with us (which is not out of the realm of possibility) I think she would be really pissed. So while this trip would be awesome--practically free, fun, and one of my favorite beaches--I think I better just say no.