Beebsy,
I am sorry about the position you have been put in through no fault of your own
It may be a bit premature for marriage counselling before your wife has investigated why she did this in her individual therapy. It seems like she has some ideas about that already, and those need to be explored and fixed if she is to be trusted as a life partner again. Responding with no boundaries to anyone who pays her attention makes her hugely vulnerable to any opportunist who can be bothered to pay her a compliment. If she wants the marriage to continue, she needs to prove to you that she has changed, and has developed better boundaries and understanding of how to deal with attention.
Individual therapy would be a good thing for you, as you try to manage your pain, and cope with emotions that can change multiple times a day. That tends to be called 'the rollercoaster' here. It will be no consolation, but everyone struggles like hell after infidelity, but reaching out, talking, and asking for support is a very wise and positive thing. That is why forums like this exist, and why this place has had tens of thousands of members since it was founded.
There are some actions that should be taken quickly to disable the potential for the affair to continue, and for your physical health.
It may be the furthest thing from your mind right now, but before you are physically intimate with your wife again, she needs to have a test for sexually transmitted diseases. For your sake, and for hers.
Your wife should start looking for another job immediately, or simply resign and then start looking for an alternative job if your finances can support that.
Her affair partner's wife must be told as soon as possible.
And as the activities were limited 100% to the workplace, from what you have been told, the headmaster of the school or the board of education can be informed.
Her going back to the proverbial scene of the crime, with no actions taken to expose the affair, has the potential to lead to trouble. What has your wife said about finding an alternative job? She needs to understand why remaining there will put an untenable strain on you and what remains of the marriage. If she is serious about wanting to save the marriage, she ought to be willing to make the changes needed.
Do you have any friends, or a manager at work, that you can talk to? A lot of times people tend to not want to tell anyone, but it can be a great help to have someone to talk to when you need to vent or just release pressure.
[This message edited by M1965 at 10:34 PM, Monday, June 24th]