Sorry you have found something like this. This is why snooping is discouraged. The old adage of "Peek not through a keyhole lest ye be vexed" springs to mind.
As you said, you always had a gut feeling that something was up. People who are cheating...lie, that's the bottom line.
She may well be hugging, kissing you and talking of the future to keep you there as a safety net in case this fantasy that she's possibly acting out doesn't work. Sorry to say but you may be the back-up plan right now. I'm not saying she IS definatly cheating but it does sound like she is in some way.
Personally, I wouldn't confront her until you are totally sure that this IS the case, and you have some hard evidence to back it up. It WILL mean snooping around a bit (which is usually discouraged) but if you need to know, you need to know.
You could just use this development to detach from her though - that's what I would do first. Bear in mind that you sat and laid bare your soul to your W, and admitted all of your faults etc. She gave you a hug, shed some (possibly) crocodile tears and said that you both had things to work on. Yet in the back of her mind she was (again, possibly) thinking about an OM. I would definatly be using that to detach whilst trying to find out for sure. If you do find out and have the evidence to back it up, you could then calmly confront her about it IMHO.
Others will chip in with their take on this, and i'm not a vet so temper my advise with the knowledge that my M is broken right now and my opinion may not be the best course of action.
Try not to obsess over it, as hard as that may sound.
Take care, Barry.
Me 40 W 38 T 23 M 21 S21 S19 D16 S14 BD 19/12/2014 D mentioned 27/2/2015. I filed 08/04/2015, D Absolute 04/11/2015