OP look at what you posted before you knew the truth. When he was still lying to you:
I have suggested going to the police and he has agreed that it may be a good idea, but that in the meantime he will get IT at work to check things out on Monday... My instincts are still saying that he is telling the truth on all this. He was horrified when I asked him outright about it last night, and after this many years married to him I believe his reaction was an honest one.
You say that your instinct was to believe him, yet something led you to post here. I think your instinct, your real instinct is spot on but in your mind, your rational mind, you are not yet ready to see what is plain to others.
I can't see that he is hiding anything. He was quite upset when we were on the website in the process of deleting his profile, but he hates anything sleazy so to me his reactions were very much in keeping with how he usually is.
You are grasping at straws. He is acting the way he thinks you want him to be and you are allowing yourself to accept this act as real.
This is what I posted to you earlier on the thread and it still stands. We will be here for you, when you are ready.
'OP this has changed things in your relationship now. You will never think of him quite the same as before, even if you try very, very hard to ignore this or forget about it.'
'It will always be there. It's quite likely that you will want more support at a later date, that you will want to talk it through when he is no longer interested in listening to your concerns.'
'That's all perfectly normal and mn will be here for you.'
Good luck.