I've been where you are. And then some. We stayed together for the sake of our kids. Things got better for a while, now we're completely stagnant again. Staying together out of duty and never learning to forgive each other and love each other is almost as bad as just throwing in the towel. It's bad for you, and it's bad for your children. This is a process, and it's taking longer for me than I thought it would. Baby steps. I am starting to feel again, and I have yet to get rid of some to the anger. Same for her, I think.
First, you've got to make the decison. Do you want to stay together or not? Then, you've got to go to an excellent counselor (note - some pastors do NOT have any business calling themselves marriage counselors - be careful). Finally, you've got to decide to stick with being an active an willing participant in this marriage, and not just dead wood, hanging out because it's the right thing to do. All of these things can take time.
Know the truth of what really happened. Did they have sex? Or was it just a kiss and an emotional affair? Was it infatuation? Or something deeper? Were you providing what she needs for emotional and physical fulfillment, or is she out of line with what she expects from you and she was living a fantasy life? All of these things will come out if you get a decent counselor.
If I were in your shoes, three things would need to happen asap. First, the other guy leaves the company, or you do. Second, I would not want my wife working there at all if he's still around. Third, out of respect for you, she should cut off contact with the other guy.
This is bad no matter which way you look at it, but if it was only a kiss and emotional involvement, sometimes that has less of an impact than if it were full blown sexual involvement. You need some time to weigh all the thoughts racing through your head. Don't do anything silly out of your anger or hurt (like see another woman). It sounds like you want the marriage to continue, so don't wait. Move forward now, get some help, and be prepared for the long process of rebuilding trust.
And may I add - look in the mirror. Sometimes the guy staring back at you is somewhat responsible for setting up the emotional framework that allowed the affair to happen in the first place. Not always, just sometimes. That's another area where a counselor can really help.
I'll be praying for you. If you need direct help, please PM me. I know I couldn't even think straight when all this stuff went down in my life, and how utterly stupid I acted through some of it. I won't commiserate with you, but I'll give you whatever practical advice I can.