Hey! I'm a few years younger and single, and I'm only just getting into the idea of polyamory with no real experiences yet, but like you and your husband I've been doing a bit of reading and research, so I'd also like the chance to compare notes, in a way :)

Some big picture things I notice reading through your post:

I don't want to make unwarranted assumptions, but it strikes me that much of your explanation centers around sex, to the point where I'm not sure if what you're talking about is a swinging kind of arrangement, or actually polyamory. Both are can be considered instances of "open" relationships, and understandably there's a lot of cross over, but they are both distinct approaches. Have you considered swinging? Without getting too personal, why is that not an option, if it isn't?

Also I would challenge an implicit assumption that I think you're making - that because your husband wants to live polyamorously, that you must as well. If you yourself actually desire only one partner, it will only cause both of you - and your other partners - undue stress to force yourself to live in a way that's not authentic to who you are. But the good news is if you don't actually want other partners, but you still want your husband to be able to explore other relationships - congrats, that's not unusual! The thing is some people are monogamous in the sense that they want only one partner for themselves, while others insist that they and their partner both remain exclusive. You could very well be the monogamous, but of the first type. Then again I don't know, you could also be poly, my point is just that you should never feel like you have to be, no matter what other people decide. (Even people you're married to!)

Finally there's the issue of jealousy - the most common myth about poly is that you can't be jealous and make it work - in reality all the things you're feeling are totally and completely normal. On average poly people are just as jealous as regular people, give or take, the really big difference is only that they've learned to deal with it. It's much the same way that I suspect you and your husband must have learned to deal with anger and arguments in your relationship - it's not that happily married couples are naturally upset less often than average, give or take, it's that they've learned ways to argue better and avoid resentment, ect. Jealous is really no more difficult to deal with, except that our culture teaches us that it is.