I think that it has to do with something I read in one of the Gottman books (sorry, Michele--but I try to find what good ideas I can find from whatever source I can!).
The book talked about bids for emotional connection. I think that we have a dynamic going on where I have to be VERY specific about my attempts to make an emotional connection, and he's not very good at recognizing those attempts and also doesn't realize the importance of them.
Sometimes I just want to shake him and tell him to stop being so LUKEWARM! I know there are strong, passionate feelings in there somewhere, even if it is terrifying for him to put himself out there and feel vulnerable.
It's terrifying for me too, but I'm doing it anyway to meet his needs better and try to build a stronger R than we had before.
I guess I'm a little frustrated, but rather than get resentful, I'm going to try to approach this as gently pulling him along with me.