STH, we've all been there. But don't be surprised by the mistakes only, no discussion of changes. She doesn't want you to change. She wants to be justified in her PA and if you change into the spouse that only a fool would leave, well, she'd be a fool to leave.
Snooping is never a good thing, but sometimes we need the information we obtain. Though I find it curious that she left her computer unlocked. Most of the time cheaters will cover their tracks, so I am wondering if she wanted you to find the messages. Either way, the fact that you can't get it off your mind is why it is generally better not to know. Now you will be tempted to discuss it with her which hurts you instead of helping you.
M(53), W(54),D(19) M-23, T-25 Bomb Drop - Dec.23, 2017 Ring and Piecing since March 2018