Thank you for requesting my help.
You and your wife are caught in a very difficult situation. Although it is common in marriages where someone has an affair, it can be very painful to work through.
Let me reassure you that your wife's feelings about having her own affair are very normal. When you had the affair, your wife was deeply hurt. She lost her trust and her special connection with you. You have since tried to work through it and bring back what your marriage lost. But she may still feel hurt by the fact that you paired up with someone else and she has only been with you. She cannot say that someone else has loved her so she can feel more validated. She can only go by you and she lost that connection with you when the affair occurred. In other words, she feels that she shared you so she no longer feels special to someone.
These feelings are not as much about you as they are about her. She sounds like she is still trying to cope with what she feels about the affair. She also may have low self esteem and the affair has made her question herself more or there is another reason she is having trouble moving on from what happened. Trust can take a while to rebuild and if there are other issues in the way, like low self esteem, then it can take even longer.
Your wife has told you that she has no intention of actually cheating. At some point, it's going to have to be a matter of trusting her unless she gives you reason to do otherwise. In the meanwhile, you can continue to work on your marriage. You mentioned seeing a Marriage and Family therapist which is great. And talking to your friend is good too. Support is very important. Have the two of you been working on this together too? It's important that your wife also has support too and maybe see a therapist herself to help her work through her own issues. Here are some other resources you might want to try:
How to Help Your Spouse Heal From Your Affair: A Compact Manual for the Unfaithful-
Linda J. MacDonald
If you spend time focusing on your wife, making her feel special, and telling her how important she is to you, she may be able to move on from the affair. Go out on dates, spend time together just talking and allow her to talk about how she feels without judgment. Accepting her feelings is a very important part of the recovery of your marriage.