Softball - I'm really interested to know how you are doing. Based on personal experience I am really concerned.

I believe you have two options. One leave, two live with this form of infidelity.

I thought I could live with it with my ex husband. I caught him repeatedly and was repeatedly told there was nothing wrong. I had reasons to suspect he was meeting these women offline. When we went to couseling and the therapist told him outright his behaviour was not appropriate he stormed off. When I left he almost immediately moved a woman in. I suspect she had been one of his many internet 'friends'

I wasted 16 years taking a back seat to his 'friendships'.

Here's this thought for you. Point out to him that if he has to hide it then he knows it's wrong. I doubt he would turn around and claim to be open about it.