It looks like you really handled this situation very well as far as discovery and getting as much of the truth as you possibly could. It also sounds like your wife might be a good candidate for R, if that's what you choose. Your attitude right now also seems to be about as on point as one could expect in your shoes. You don't have to commit to reconciliation right this moment, or ever, if you don't want to. I think keeping the door cracked open for divorce is fair in your situation and there's nothing wrong with playing it day by day while you monitor your wife's behavior and actions as you decide how to continue moving forward.
I hear you loud and clear on actually seeing all of the evidence that you've seen. I, too, saw a lot of communications through text and FB chat that I wish I hadn't seen, but like you, I had little choice but to investigate if I wanted the truth. Because my wife wasn't very forthcoming at first either. She said some pretty hurtful things to her friends and AP in service of justifying her actions. Some of it was true, some exaggerated, and some was flat out false. Again, like you, I'd never looked through any of her stuff like before in the 26+ years we had been married at the time. It was very painful. What I didn't have to see, because there weren't any, were pictures, images, or videos. I don't know if I would be able to recover from that and still want to stay in the marriage.
As far as the crap rattling around in your head right now, it's a pretty normal response to the trauma you've experienced. I'm just going to piggyback on others suggesting individual counseling for you. I've heard good things about EMDR therapy for getting over stuff like this. Another thing that helped me a lot wss just posting and venting here. There are a lot of good, understanding people here who know what you're going through, and talking about itnwith others has helped me a lot. Don't be afraid to just vent if you want to get something off your chest. Keep posting and hang in there. Time is king and it will get better with time.