<human>: I am having some conflicted feelings right now, and I don't see how she can explain herself out of this one and I think the only option is to break up with her.

 While I was playing around with my girlfriend's phone that she just bought a couple of days ago, I saw a Facebook message that popped up from some guy telling her that he loved her. I'm not one to snoop, but I had to see for myself what was going on. Not much communication, and they're not even facebook friends, but it was obvious that they knew each other. The one post that really bothered me was the one where she told him that she loved him but to never tell me (after the message that he sent her). That was all I looked at but I think that was enough

I'm definitely going to confront her about it, but I really don't see any possible innocent explanation and just looking for opinions, please

Could you distill the essence of the text into 1-3 sentences?
<bot>: saw a message pop up on my girlfriend's phone that caused me to snoop - her and another guy telling each other that they love each other. I am looking for opinions on if there is any chance of an innocent explanation