This is also my question/dilemma

I have this same question, is it too late for a proper discovery process? My husband's affair was years ago (2002 - '03) and he claims it was very short (less than a year) but I believe he is not telling the truth. I believe he was involved with her up until 2013. I have uncovered many details on my own, that when put together make a very strong case that I am correct. When I try to discuss this with him he blows up and says he "told me everything", or "what more do you want from me", or "get over it." He acts as if I am crazy.
What I need to know is the extent of his affair. there is a big difference between having a six month fling and an affair lasting years. How can he say it meant nothing when he continued to see her over a ten year period. To me, she must have meant more to him than he is letting on. I have a problem with this aspect of it and this lack of truth makes it hard to give myself fully to this marriage. It is hard to forgive if you don't know what you are forgiving. He does not understand this when I say it, or at least he doesn't want to try to understand.

So, my question is: Am I wrong for bringing up what he says should be left in the past or is it fair to expect truthful answers to my questions, regardless of how long ago it was?