hangingin - I agree he is trying to re-direct blame - and not just with this. He is trying to make you feel obsessive because you have a better memory and timeline to him.
I'm so sorry that he was unfaithful when you were ill - but I'm afraid that speaks volumes for the sort of man he is. And it only stopped when OW ended it, so he didn't even choose to return to your marriage, but you let him. I also have to say, I think it extremely unlikely he remained faithful in the interval, especially given the way he is behaving now, actively pursuing a relationship with someone else.
Hangingin, I understand that emotionally, you cannot cut your ties with this man, although I'm sorry that is the case. However, can't you act as though you have? Honestly, it will do wonders for your self-esteem if you were to tell him that you're putting the UK property on the market/out for rental and will be finding a home for yourself, so that you can start a new life. Tell him you're not going to waste any more of your life and are open to meeting someone new.
And don't think for a minute that you wouldn't meet someone new - you are in one of the best positions in your life - child-care free, independent, economically solvent. You are a great catch.
He's got absolutely no incentive to change things at the moment while you put up with this. He's lost empathy for how you are feeling. So you've got to stop giving him the appearance of hanging around waiting for him and move on. If you've fought breast cancer, you've faced worse battles than this. You are strong.
At the moment while you still love him, you can't see what life would be like without him. You didn't answer my question about who had been the over-benefitted one in your relationship, but tbh, you don't need to - it's bloody obvious - it's been him. That's not good HangingIn.
Would you consider some courses/ counselling to work on that self-esteem of yours? You must have got the point now from all the women on here that we couldn't tolerate this - and I really do think the only reason you can is because your self-esteem is at zero.
Act tough even if you aren't tough, is my message. Your H's behaviour screams of over-indulged entitlement and I'd say the rug needs to pulled from under his feet, even if it is 20 years too late. Better that than face yet another episode of this in 5, 10, 20 years' time, because believe me, it WILL happen again.