I have a relationship question I need some opinions on. A little background first. My girlfriend and I have been together for just over a year now, we've been living together for about 11 months. We are both college students but go to different institutions. About a month after we started dating she admitted, without me probing, to kissing another guy, apparently felt bad and promised to be loyal to me from then on. About six months after we started dating she admitted to occasionally exchanging of nudes with another guy through snapchat, she had been since before were were going out but was feeling bad and said she would stop, which I believe she has. Now, last week I told her how I felt about spending lots of time with guy friends from school, I told her I didn't like it because she's spending more and more time with them, sometimes into the evening, and I haven't even met them. When they hang out they're tanning, drinking (either going to a bar or at his dorm/pool) or playing volleyball. She admitted to being attracted to one particular guy and flirting with him. I asked her to stop flirting with him and anybody else because I felt disrespected, she understood and agreed. But this morning when I asked her what her plans were she told me she was going to hang out with those guys after classes but she should be home by the time I get home. She wasn't. I got a text from her just before I got home saying shes tanning and drinking so was hanging out later than expected.
So my question is, should I be worried? Or am I being over reactive, and trust her to just hang out and not flirt with that guy? I don't wan't to push her away.
Thanks for any advice