He is denying it and has deleted the evidence so he doesn't have to confront the problem.
The longer this goes on the more you'll doubt yourself and wonder if you definitely found what you did and then eventually everything will go back to normal for him.
Its called gaslighting.
Fab is a casual sex site, you can live cam with people (watch them having sex or masturbating) and watch videos etc but most men would go on pornhub or such like for porn.
He is never going to admit this, my ex husband denied his emotional cheating despite me seeing the messages, he would delete everything and smash his phone up and still deny it all.
Until the next time and then he would admit the previous time but deny the current time.
Its gaslighting. I stayed for 17yrs as he threatened to kill himself but eventually left 3yrs ago.
I've been on Fab for a while, its full of married men.
You know he was on there, you know he had a photo on there, what more proof do you need? You can end your marriage at any time for any reason.
You don't need him to admit to anything.
What do you want to do?
What kind of husband is he generally?