Well, I am so sorry you are here. My FWH had an emotional, text, email, facebook affair, too. I found out by finding a video in his email that she sent him. It was disgusting, and I, too, went off the deep end with anger.
I think the first thing you should do is focus on YOU and what you want. These decisions do not have to be immediate, nor do you have to put a timeline on figuring out what you want. Do you want the WHOLE truth? If you do, make that a condition of R. Make sure that he KNOWS the lying and trickle truth has to stop, and if he can not do that, he needs to leave. I told my FWH that if I found one more lie, if he did not start telling the WHOLE truth, I was done. And, I meant it. Definitely follow through with whatever you decide.
Contact with her has to stop. Has he done that? He needs to cut ALL ties. Block her number, change his number if he has to, block her on facebook, and change his email address if he needs to. Whatever it takes to cut ties. I know he works with her, is that something that could change? Is that something that YOU need in order to consider R? The day I found out was the day he blocked her on FB, closed his email account, and we changed our numbers. He gave me every password/passcode he had, and I started monitoring the phone bill. That was the ONLY way I was going to stay, and he knew it.
There are a lot more things I could write, but honestly, I think your initial plan of action would be to figure out what you want/need at this point, and if you are willing to R. THEN, if you are, set clear cut conditions of R.