I can relate to what both you & Pink say - and sometimes question if it will always be so much "work." On the other hand, when I am feeling more positive, more generous, I can see that SO has in fact changed a fair bit - he has responded to changes in me - he has grown & opened up a bit more. But I often miss those changes because they don't look 'obvious' or like my changes.
I also find that once he gets comfortable with a new pattern or change, I have to be the first to dip my toe into the next level. I do think that he still perfers comfort, the known, over daring to risk another level of vulnerability and change. But if I'm willing to take the risk first, he often follows - not always, but often...
I think reminding ourselves that we are here by choice is a good way of keeping our focus on improvement, not resentment. And reminding ourselves to be open to see changes expressed in different ways is also helpful. I see myself often getting stuck with expectations of how he 'should' respond, change, behave - and it usually doesn't work!