I was going to mention that it might be best to talk to genebean because she's a poster here as well, and it's a possibility that she could read this blog before you get the chance to bring it up to her in person.........obviously I was a little late, lol.
Now, I've been in a similar situation. It was a tad worse because my SO became privy to the conversations I had by doing the same kinda thing, snooping around. So we were both upset for very different reasons.
I'll just say this: before anything can happen further, be honest. Just lay it all out on the table, even if it doesn't seem like much because it's been such a short period of time. But now that genebean knows, answer any questions she may have and emphasize that it doesn't change the agreement y'all have, or your feelings for her.
We will always hurt people we love. That's a fact of life and it can't be avoided. What CAN be avoided is the WAY in which they're hurt; being honest and forthcoming before any action can be taken is a path you can take to do so. Just to put it into perspective, if I was more concerned about hurting my ex by breaking up than about my own sanity and well-being, we'd still be in a relationship and I'd be more unhappy than ever. We're still friends, btw.