First off I am sorry you are here, but this is a good place to come if you are in your position. I have only been here a short while and have found some excellent support. Most people would want to know some more information about your situation (how many years married, circumstances of spearation, kids, etc) basically trying to get to know you. One other thing people find helpful is to kind of setup a thread like this one to be "your thread" so people can follow your story.
Just on inspection I would guess there might be something with the OW, possibly an EA that he doesn't even recognize as such. I had one a number of years ago that started off as friends until I woke up one day and realized I had feelings for this person.
Do you and your H have any mutual friends? If so if you start to GAL and start working on your self, it is likely that word will get back.
I really don't want to suggest anymore since I don't know too much and am relatively inexperienced at this whole game. You will likely find some excellent advice from some of the more experienced people.
TwinDad Me 39, W 36, M 11 W - MLC, WAW???? 2 Kids B/G 3 YRS Old Start of the Long and Bumpy Road..... On the verge of piecing.....a new beginning