Wow, lots of karma on this thread...

I don't know if you can get through to your husband or not, but if you try telling him that unless he is willing to tel the truth about the affair and show by his actions that he knows how to avoid having one again in the future that you will NEVER let it go. You might move on, but will NOT be able to forget that it happened.
Dr Harley has said that those who have experienced both rape and betrayal by their spouse have said that the betrayal was more traumatic than the rape. Those who lost a loved one to death, even a child, claimed that the betrayal hurt worse than the loss in many cases.
In order to actually recover from an affair a specific plan must be in place. This plan must include never seeing the affair partner ever again, but it must also include a method of ensuring that no other affair partner can ever enter the picture. This can only be done by putting into place extraordinary precautions that make a further affair unlikely if not impossible.
I can tell you that unless the affair is examined and understood, not why it happened but how, that you will never feel safe to let your husband have full access once more to your heart. And this will make your marriage less likely to be able to avoid future affairs by either of you than resolving the problem rather than avoiding it.
Read this:
Joseph's Letter and see if you can get your husband to read it too. I suggest printing it out for him rather than sending him here right now.
Sorry you are here, but under the circumstances, it is a wonderful place to be, though none of us wanted to be here in the first place.
Mark