I must say, I'm a little shocked. This view of your H's that your M may not be "fixable" as people can't change is a very harmful one!
I suppose you, of the "towering intellect" (not sarcastic, just another similarity we share ) know exactly what you need to do now..PROVE HIM WRONG!
I KNOW you can do this. We are so similar Sage, and I've done the very same thing. In fact, I believe that my genuine internal changes are part of why H and I are still together and there is real hope here.
I think your conversation, painful though it must have been to hear those words, is a definte step in the right direction. Particularly since it didn't end with him just throwing in the towel!
However I have great empathy for you, too. Why can't he be strong enough to comfort you if you burst into tears? So you are an anxious person by nature, shouldn't your S be your "soft place to land?"
Of course these are all feelings I too share, but my H seems a little better at accepting at least the anxiety and sadness (not so keen on the anger and sarcasm...but then those things I've been dealing with rather well).
So... Ms Sage with the "style" we all admire so... what will your new goals be? Prove him wrong, Sage, Do it! And not just for him or your M, but for YOU! I feel like a much better, stronger person for all of my changes and I know you do too. He just needs to be convinced that it is possible.