You are very welcome. I love this forum because the majority of the members are open and more than willing to help with their thoughts on any kind of matter.
One of the reasons why I'm personally holding back in sharing my own speculations right now is because I don't want to color what discussion you will have with your wife. I want her to be able to say what is bothering her instead of you offering options as to what it may be and having her pick one that may not be true or only part of the truth.
Have you two done any couple swapping? Hotwifing and MFM are different from couple swapping. Part of her not understanding how men enter the lifestyle with their partners might stem from only hotwifing/MFM because she has not come from the experience and growth that can come from couple swapping.
Three points that do worry me a bit...a husband's persistence in a asking/suggesting something of their wife (especially for years) can lead to several feelings if not openly communicated about. It can be construed as nagging, which can be ignored or not. It can be a, "What can I do to shut him up?" or "When will he stop talking about it?" During your years of suggesting it, were these always during foreplay/sex? Was this ever discussed outside of the bedroom? How did she react about it every time you talked about it? Was it a constant "blah" or a gradual progression of excitement? Did she ever ask you to stop suggesting?
Another concern is that you said, "We used to read/send emails together." Does this mean that you stopped doing this after awhile? Did you only do this when first contacting others?
Lastly, how did you two find these men? It sounds like they are not part of the swing community, which means they may not understand the complexity of a couple that hotwifes/swings, which can be very problematic. They may have this idea that the husband can't satisfy the wife. Or that they can woo the wife away from the husband.