KINDLY EXPLAIN THIS PART OF YOUR OST AS I DID NOT UNDERSTAND THIS: “So while a little what-if thinking is ok, in fact i normally recomend trying to reach decisions in advance when your not entrenched in a particular moment, It would pay to keep tabs on yourself and make try to make sure that you dont sink into a game of what-if with yourself, of second guessing every littel thing thats happened and that might happen in the future.”
What im suggesting is that before you reach the point where you have to make a decison about something that you have already worked out what the criteria are for that decision. Trying to determine the criteria and make the decision simultaneously can lead to major influencing considerations being 'forgotten' of left out. We also tend to want to bend the rules a little on ourselves.
So thinking about what might happen could be useful in that context of trying to decide what factors will enter into your decision of whether you want to offer her R or whether you want to persue a divource.
However, for the sake of your own sanity you should try to as much as possible not constantly dwell on thinking it through over and over again, running through all the possible things that might happen... doing so is a cruel form of self torture in my opinion.... of course its easy for me to say dont do this, and to be honest i also struggle with playing what-if with myself, but when i catch myself doing it i tell myself that the only person that suffers from it is me, and i try to change my train of thought.
I hope that helps explain a little better, if its still unclear pleas feel free to send me a private message.
Brother its only natural to secondguess your initial reaction. I initially found out about my wifes first A through her diary, some 2 years after it occured. In it she described meeeting this guy making out, spending the night in a hotel, even that in the following days she had trouble walking 
The day after reading that i had almost convinced myself that it was just a fantasy, that she had written it too punish me if i should ever read her diary, or because she was trying to write one of those 'womens diary novels' .... until i checked out the name of the town, and hotel she stayed in, a little place that she would otherwise have never even known about.
Your mind is playing tricks with you, its in such turmoil that if it can just get you to believe that its 'nothing' then things can settle down and you can feel safe again. This self inflicted gaslighting is almost as cruel as the gaslighting that many BS's get from their WS once they do confront.
unless your W is someone that uses an overtly affectionate tone with everyone she is friends with then youll probably not find anyone that would say that these emails are at the very minimum overly familiar. At the very least these indicate an Emotional Affair with this man. My (as a result of all this) now cynical nature ould say that as adults if there is the desire, and thir has been the opportunity, then the EA will also almost certainly have been consumated into a full PA.... the sad thing is that even if it hasnt an EA can be just as damaging (i think even more so for a WW) than a PA.
Good luck, look after yourself, make sure you are getting some sleep, make sure that you are eating at least something, keep your wits about you.
