It is difficult
Journey,
The situation you are in is extremely stressful, difficult, and with long-lasting consequences, regardless of what path you choose to follow. After reading all the pages of this topic, and seeing the heated discussion, I have a few observations which you might find useful.
1. When a poster offers a personal story in a public forum, he or she purposefully avails herself to sympathy, advice, criticism, and even ridicule. While it is "nice" for people on message boards to be polite, this is not always the case and it is your job to sift through the information given to you, pick the small nuggets and make the best use of it. I have seen posters (especially on other boards) receiving much harsher treatment than the one here. I commend the community here for remaining, by and large, on the side of the civil. Also, it is better to hear a harsh comment for the first time on a (somewhat) anonymous board so you have time to think it over and come up with an answer, than having to face it unprepared with people who are important to you in real life.
2. People who share any form of alternative lifestyles (poly, swinging, BDSM, kink, etc.) come from all walks of life. Thus, you meet cross section of the general population with all of its good and bad. People will respond to your input in a way that is consistent with their own experiences and capabilities. Some will be helpful, others will not, some have issues, yet others have profound issues (that is my observation from people I have met in real life in the alternative lifestyles, not anyone on this board). Keep in mind that people in the alternative lifestyles are very often simply “different minded” and not “open minded” despite what they say. So, take anything with a grain of salt. The ultimate decision is yours.
Who are parties to consider in this situation?
Is it 1) you; 2) you and your husband; 3) you, your husband, and the community you live in; 4) you and your husband in the "potential field" of the community you live in; or something else? The answer to this preliminary question will help you find the remaining answers.
3. The 60 years. There is a book called “Men are from Mars, women from Venus.” Without going into details, people use different expression means to convey a message. The “60 years” can be simply translated as “something that feels to be an unreasonably long time” especially when said in a moment of distress.
It is Normal, for Normal people, to act Abnormally in Abnormal situations. For someone who is genuinely monogamous and who doesn't even have a remote experience with poly, being introduced to the possibility of having to change his life on day to day bases toward poly could be an abnormal situation. Thus, abnormal reactions are to be expected.
Let's consider the effect of the community in which you live. There are places, where the man, the husband, is deemed ultimately responsible for the well-being of his family, no matter the circumstances. In such a community, your husband will fear that he will be looked, for the rest of his life, as the one who failed his wife so miserably, that not only she left, but also she lost her faith in marriage and monogamy. In his fears, his community will see him as a leper, always being “the man whose wife . . . “
4. Bait and switch. It was sad to see pages of arguments over this because your situation is incredibly serious and this argument was like time spend on rearranging chairs on the deck of the Titanic. Your realization what you want to pursue polyamory introduces a profound change in your family. Unless both parties arrive to the same page, the experience is likely to be very traumatic. It matters not who said what a number of years ago. The thing that matters is that you are faced with a fundamental change that will alter the day to day living to one or both of you. To make it more clear, there are similar, non-sexual /amorous, changes that could be traumatic.
Some examples: 1) one spouse decides to convert to a new religion and takes is very seriously; 2) one spouse gets burned out on the corporate job and decides to move to a humanitarian mission in a “third world country”; 3) the son in a Reform Jewish family decides to become Orthodox, puts the black hat and tells his parents that he can't eat at their home anymore, etc. etc. I hope this gives you the idea in common - the rest of the family has the “option” to “accept” or bust. Regardless of their decision, their day-to-day life is not going to be the same because they will either lose a loved one or will have to change the way they live.
The very same thing may occur in a swinging couple when one spouse decides to become “born again” and tells their "sinner" half “honey, we have to talk . . .”
5. There is the possibility that your husband has understood what poly is, disagrees with it, but can't express himself in a way you can understand it. Some people claim that as long as you can make somebody see your point, he or she will accept it. This wrong and very misleading, if not worse. Lifestyles are a matter of personal choice -- a taste. One cannot argue a taste. You either both share it it not. A small number of couples can arrive at the mono-poly arrangement but this is by far not the norm and often the circumstances won't allow it even with the best of intentions.
6. No matter what you do, it is a good idea to think it carefully, with as little motion as possible. Try to do a “though experiment” and imagine the likely possible outcomes. What will happen if you leave? Imagine that you are already divorced. How you will approach your first year of being alone and able to explore. How do you see yourself in 10 years? Happily married to a poly partner with a few other loves and friends? Or alone and down on her luck, asking yourself “why did I do this to me?” Live is full of treachery and we often don't hear about the losers because their don't stick around to tell their stories.
7. I will suggest, at least in your thought experiment, to be extremely selfish and think hard of what is the best for you in the long run: 10, 20, 30 years from now. There are components: physical, material, emotional, social, spiritual (not necessarily religion based, but being in peace with yourself) and all take part in in your equation of happiness. The tricky part is that the equation of happiness is a time-dependent function and changes with time, as you have discovered on your own very recently. What can you do so that you are happy many years down the road?
Best of luck.