Scared, listen to what everyone is saying. First, no one is saying that your W IS having an A, just that she MAY be having an A. Don't let your imagination start running wild.
If you agree with these opinions and you suspect that she is, you need to find some evidence before confronting her as suggested.
Many of us have gone through the same thing, so you are not alone. So as Bond said, this is an important time to get the support offered here. You may hear stories that frighten you, but remember, those are also not necessarily your story. Just information that may be useful to you.
I know it is hard, but try to stay calm and sane. If you let your emotions control you, you are bound to do something you regret.
Take care.
BITS
Happiness is not something ready made. It comes from your own actions.