What to do with evidence of an OM?

So I "happened" to find more than a few emails on my W's computer of at the very least an EA with an OM. Really painful to read as it was happening while we were still living together. To my face and in writing she has maintained that they are just friends. I'm not 100% sure if it is a PA or not but it's painful nevertheless.

Is there ever a good time to confront her with this? Do I just try and forget about it as I shouldn't have seen it anyway. The lying and denial I can't take. She's placed so much blame on me for our breakdown in our marriage and yet she does this. Her anger at me seems to be to justify herself and diminish her guilt. Such BS!