<human>: Can you provide a brief rundown of the text in within 3 sentences?

I was using her computer and a Skype chat log was up. About two months back was a chat between her and her ex that was rather sexually explicit, and I'm absolutely devastated.

 When confronted, she initially tried to shift blame, but eventually apologized. She said that it was stupid and childish and she was just seeking attention. I have a feeling this wasn't an isolated incident, but she denies that it goes any further or that it was also a physical thing.

 What really kills me is that I'd brought up pretty much this exact thing as a source of insecurity for me, and she'd repeatedly assured me that while she did talk to her ex she no longer had feelings for him, and I feel as though she's been lying to me this whole time. I really want to forgive her and move on, but I'm not sure I can. I still love her to death but I can't have this thought be in my mind and continue my relationship.

 Any advice or comments would be greatly appreciated.
<bot>: My gf of 2 years has had at least one sexual chat with an ex, how can/ should I work to fix the relationship?