Girlfriend wanting weekend away with guys?!?

Me and my girlfriend are in love. In the past few months she has lied to me twice about giving her number to 2 guys. I saw a conversation of one of them and they were flirting and talking about doing 'stuff'. I dont really trust her. We have different spring breaks and this break she wants to go about 1 and a half away from here with her girlfriend and party/get drunk with a bunch of older guys. theyll be sleeping in the same area to. i ume same house and/or rooms?? I do not trust her at all. I cant force her to not go. Ive told her i dont want her to go but she doesnt listen. what do i do?