I 29M saw some things in my GF’s 26F group chat that made me uncomfortable. Need some Advice

I'm a 29M, and my girlfriend 26Fand I have been dating for a little over a year. I asked to use her Mac to record a legal conversation. While I was recording, some suspicious messages started popping up, which prompted me to check the messages on GM. She had been talking with her friends about how much she enjoyed the sex from a hookup a couple of years ago, and basically how she was daydreaming about it at work and some other vulgar stuff around that subject.

I brought it up, and she profusely apologized, cried, and said she didn’t mean it and it was just her friends egging her on.

I want to believe her. She has been perfect in our relationship in every other way, but I can’t seem to get over this. It’s really messed up my view of her. I love her, and has been perfect in our relationship which is why I’m hesitant to end things.

I told her I need some time to think, and was thinking about ending things or taking a step back for a little while but really do lover her. she’s been staying with friends for the past two days. She’s been writing love letters and doing other things that are making it hard for me, but I’m trying to stay clear-headed.

Any advice for this situation?