Is she cheating?

Me and my snicker bar (aka my girl) have been together for a while now. One day my best friend happen to say she found my girlfriend flirting with a boy in the hallway. I went to confront her about it but she said nothing happened. A few weeks later when I was using my snickers phone to call my phone (since I’m dumb and lost it) I happen to see that she had called that boy ALOT of times when I was out. So while she wasn’t paying attention I went through her texts and found what could be her flirting with that dang boy. Now that I think about it she hasn’t been as supportive as she use to be. When I need her to make me happy she usually says something along the lines of “You don’t need a Damn compliment” or “leave my alone already.” I don’t know what to do and I need your girls opinion. PLEASE HELP