Am I being insecure??

My girlfriend decided to bring in the New Year with here "girlfriends" this year. I wasn't thrilled with the idea but I didn't want to be selfish so I told her the choice was hers( We have been fighting a lot lately and she claimed that the purpose of the trip was a Vent-Fest for and her friends). I was a little skeptic of the whole trip but I decided to trust her. She never called me during the time she was with her "gf's" but only texted. I found this odd so I called 3 mins after her last text at 8:30pm and didn't get a answer or return text until 11:00 am the next day once she arrived back in town. I never talked to her during the time she should be with her "friends"I feel she really went on the trip with another guy. Her excuse was she was drunk and didn't hear her phone and she said she ped out. I'm thinking of calling it quits but she came by today in tears pleading she'd never cheat and despite what it looked like thats not the case. I don't know if her tears are from quilt or she's telling the truth and is in fear of losing me. Help!