FarawayGran, I'm so sorry about your cancer and, also, your concerns about dh. I agree with those who feel the cancer is causing you to dwell on the past more than ever - what dh might have done, what your mother said, etc.
I'm a little confused, though, about whether it was just one affair or if you think he has cheated again since then. Was this one foolish mistake years ago or do you feel he's an unfaithful man, period?
Like yourself, I don't see what good talking to him will do if he's just going to deny everything. Maybe it would be good to get your feelings out there. But I sense you want an apology, and I don't believe your going to get one, let alone an admission of guilt.
So I'm joining those who say to discuss this with a counselor. Get some help sorting out your feelings. Then you can decide how to go forward.