Well, to put it bluntly, you sound like you have your shit together.
Even when we have our shit together, poly is still full of ups and downs.
For most of us, it is thinking outside the box we were ever taught. This causes the highs and lows you are starting to experience.
It sounds like your husband communicates his thought`s to you very well. If you are having problems coping, Is it might be because you take his feelings on for yourself ? Love can do that.
He stresses,...so you stress.
He`s ok,..so you are ok.
You might be feeling like you just need to know wether its green light or red light, so you can then know where you stand. For him, it`s not so simple. He might want to try, but moments of doubt might cause him to recoil. If he is the type that likes to think outloud, then you get to hear it all, and it can feel like a lot to deal with.
Thats a very normal part of being a couple.
As you get to understand poly more, you`ll probably hit a point where each of you is able to express your feelings to the other, in new ways that don`t start the roller-coaster syndrome.
It`s one of those things that can`t really be taught. It`s learned through trial and error, and experience.
It sounds like you have a good opportunity, and environment though.