There will be floods of cheerleading and advice that will come to you from this site.
Listen carefully. She is being very honest with you about her feelings. It is hard to accept. Please do see her as finally being honest. Go to the boards on Mismatched Libidos and the one Married withoutRomance. You will find much knowledge there.
Now for the no so good: A regular counselor is not trained for these things which call for one who is also an MD and a sex therapist. When you say she has "met" this guy did that mean "in the flesh" or on the internet?
If she has not met in the flesh then I have a BIG WARNING:
These people search for their prey and are very good at what they do. http://www.ic3.gov/complaint/default.aspx
Now you have some information. I suggest copying everything that you legally can esp the "headers" of email. use Yahoo e mail which keeps transmissions.
Continue to concentrate on you and your son.
"If something cannot go on forever, it will stop." Herb Stein