C.R.
Welcome to this now very big ship that many of us are on. (We have graduated to something larger than "being in the same boat").
I was maried 34 1/2 years with 4 children when i caught my husband having phone calls, "business trips", emails, etc. You must admit that you had an inkling as to something being amiss. His sudden new confidence, different attitude, secretivness, etc. NEVER let on what else you know. Save it all, though, for the atty. that you may need down the road.
Now, that he knows you are on to him, he will be more careful, more secretive. How do you know that he doesn't have a Yahoo account that you cannot check?? Men are very resourceful. You might suggest counseling but you will need to know that he is sincere. My husband didn't take me seriously that i would end the marriage until her saw the QDRO and was told to move out by the judge.
He is on the outside now looking in. The children don't call him, I don't call him, and he won't know his grandchildren very well at all. very sad for a man in his late 50's. Oh, and by the way, he now has a live-in girlfriend. It didn't take him very long to move on with his new life.
best of luck. Remember, trust and verify.
C. in Woodstock