Ray -
I think we exhaust ourselves into acceptance once we feel we have questioned everything we think possible with the resources we have at our disposal. We accept that we've uncovered all we can so our focus changes to living with it and learning as much as we can to obtain the best quality of life. We begin to trust doctors more, because through this forum, we've learned were not alone and there are many others like us.
Then we hear a new speaker, new test, improvements on genetic testing, or a miracle diagnosis or cause, and we have a resurgence of wonder or hope which gets us questioning again for a bit. I don't think any of us want to completely abandon hope - we just can't be consumed with it any longer. I agree with your partner that it's only natural for us to mourn at times - we have lost an awful lot and it's hard to watch people run, bike, dance, and do things we can no longer do. But like good old NJEd coached a few times, we focus on what we CAN do, not CAN'T do!
BTW - Why does your Neuro say your PN is progressive? We have all been through so much and all the words swirl at times, but I'm wondering if there was a test for "progressive"?