<human>: Can you summarize the given text in a few sentences?

My girlfriend and I are both in our third year of college, and have been dating for a year and a half. We are very close, and spend a great deal of time together. (quite possibly too much?) Our sex life is decent, but used to be a lot better, and she often complains that it's not very fulfilling anymore. I feel the same way, but neither of us know exactly what's wrong. 

Anyway, long story short, about a month ago I saw her sending sexual facebook messages to a friend of hers from her hometown - flirting with him, even asking for a video of him masturbating. I confronted her, and she broke down, promised to never talk to him again, to go to counseling, etc. I decided to give things another shot, though I occasionally second-guess that decision. 

A couple days ago I was looking for something in my browser history and saw that when she had been using my computer, she was on "Facebook Messages - [his name]". I plan on confronting her about it today. I suppose there's a chance it was a one-off thing - maybe he sent her a message that she read but didn't respond to, or responded to saying she couldn't talk to him. What I'm wondering, though, is that if that's what she says when I ask her about it, is it fair of me to ask her to log in to facebook and show me that she's telling the truth? I would feel bad doing it, but I also wouldn't totally trust her answer otherwise. 

I also wonder if breaking up with her would be the right thing to do if she is talking to him again. She was friends with him for a while before they started flirting, and if she was just talking to him as a friend I don't know if that's far enough over the line to justify a breakup. All the same, I know if she'd lie about talking to him again, she'd lie about other things, and I don't want to be dating someone I can't trust. 

Thanks for your help.
<bot>: Girlfriend might be talking to the guy she cheated with, is it appropriate to make her show me the messages to prove they're innocent?