Is my girlfriend cheating on me?PLEASE HELP!!?

First off all she has three of these guys that shes really close with and they go camping at the same place She always says that she loves me but she is always on the phone and online with at least one of these three kids She goes camping to this place alot and a few weeks ago she snuck in there to hang with these kids I was told by her bestfriend that my girlfriend told her about all the things they did Her bestfriend got a call from one of the three guys while my girfriend was with them and he told her that my girlfriend and him just did it But when i told her what i heard she denied the whole thing And i just got a call from my bestfriend whos at the same campground and he told me that everyone keeps tellin him that my girlfriends sending naked pics to people. and she denyed it once again While i was lookin at my gfs phone i saw pics of one of these kids sixpack So im startin to think that they sent pics to eachother and hers got out. pleas help!!!! i love her soo much