thats tricky......you gotta understand, most women are INCLINED to cheat. especially more than men, just because of the fact they think on emotion and all rational thought escapes them.
on the other hand...i know plenty of girls that have very few female friends and mostly hang out with guys. From my experience these girls have been the most faithful. These girls often send the wrong signals to guys because they're very friendly and open with them (i know because this happens alot lol)...So the guy may THINK she's interested but in actuallity he's just a "buddy". i'd try to meet these "guys" first and then try to get a reading of what vibe they give off. Maybe they're just pussy ass kissers trying to get some ass from her but she wants nothing to do with it.
i dont know how your girl is so i cant make a judgement but if a girl is cheating on you she will do ALOT to hide it. by openly telling you where she's going i think you may give her the benefit of the doubt. but like i said, meet these "friends" and make the decision for yourself