This ordeal has been so hard on you that it has been difficult at best to move forward. Tell him that you understand his reluctance, but you need the healing. You were the one who was injured. You were the one who feels like this is being swept under the rug.
Tell him that this is not to punish him. Just you at uncomfortable the way that there has been no real closure and growth that is necessary for both of you moving forward from his affair.
It is really important to have help in this and not just let things not get worked out.
