You really need to get that divorce started for your own safety. You need financial arrangements set in stone and the joint accounts closed totally. Finding cards and hiding them only solves issues temporarily.
Throw your energy into getting yourself sorted. Get three house valuations, so you can provide them to solicitors, change wills, find out what mortgage you could take on alone etc. Pack all his clothes up and put them in the spare room (when I say pack, I mean dump them in a corner, tip the drawers out, whatever, to make it so he doesn't have to come into your room for anything. If it's all sitting there when he comes home he will get a clear indication that things are going to change, even if he doesn't think they are. Tell everyone. They will all be shocked and mostly on your side. He will be ashamed and guilty for a short time only. Use that time to get everything sorted. When my cheating ex first confessed I was a tearful, broken wreck. When I saw him a week later I had had the house valued, seen a solicitor, made lists of what belonged to whom to divide the household goods up, and it knocked the smug wind out of his sails for a while. I know it's horrible and you're hurting, but doing things like that gives you back control and power again, and it feels good.
And next time he says "why didn't you say?" Reply that you were hanging onto the hope that he had more morals and wouldn't be so disrespectful in his disgusting treatment of you.v if he brings up that he'd felt like this for ages tell him he should have had the decency to say something, not just gone off and found someone else to shag. And when he says they have more in common reply that they certainly have low morals in common. Do not let him throw blame at you! He is to blame, 100%.