OP it's not true remorse you're seeing at all. It's fear and a hope that everything can go back to normal.
Please do get your own STI screening and talk about the risks you've potentially been exposed to with your cancer specialists.
I think you're probably both in the 'denial' stage, but this is why it's very important to talk to others about what you're going through, in order to make it 'real'. At the moment, you're in a bubble where you can almost convince yourself this hasn't happened, because on the surface, no-one would know any different.
But for your husband to truly acknowledge what he has done, he needs to face up to people knowing about it because right now, he can also pretend this never happened.
The person who caused the pain can't be your comforter; it's a conflict of roles that will damage you. But you do need your own source of support in real-life because with the the best will in the world, cyberspace cannot hug you and dry your tears like a good friend might.
Please consider getting some space from him and talking to someone who won't judge you for either wanting to leave or to stay - and who doesn't have a vested interest either way in your decision.