My sitch is not similar, but I've been sitting here trying to think what I would do. This advice might not be the wisest move, but it might be somthing to consider. Although, I imagine there it's lots of good advice on some of these sites that offer information about internet relationship addictions....
I think, if I were in your position, I would probably admit to my husband I knew about the relationship. The addiction may be too strong, and he might not care if you know or not, but my suspicion is it will only get stronger either way. And your knowing may make it a little less comfortable and defantisize it a bit. My fear would be the longer it goes as this hidden fantasy, the stronger it would get and the more damage it could do to the marriage.
On the other hand, him not knowing allows you to monitor the situation.... so him not knowing may be something you don't want to lose. Espcially for any possible "meeting" they arrange to have. This I would definitely show up for... and I might even bring the child along too!!!! That could be a real romance killer....
Quite honestly, him meeting her in-person maybe the thing that kills it. Possibly...
If he does somehow learn that you know about the relationship ask him how he knows the woman is not a man? Maybe it's some old dude pretending to be a woman??? How does anyone know who any of these online people are? Heck, she's probably some 600 pound bedridden man, or some 90-year-old lady in a nursing home.
Another thing....I'd probably be tempted to secretly join the stupid website they are "married" on and become one or their buddies so I could infiltrate the relatonship and somehow destroy it. Maybe become your H's 2nd OOW!!!
There is no arriving, ever. It is all a continual becoming.
