R"Either way, what I miss is who I thought he used to be (whether it's what I thought or what he actually was maybe doesn't matter at this point), not who he actually is now. "

I have/had the exact same issue with my STBXW. I think even others here pointed it out. I know family and friends did too. I still struggle with it. I am sorry for your pain.

me: 47, W:49
M 16.5 years
T 17 years
Three kids - D17,D14, S13
Heart 2 heart about M 11/8/13
Bomb drop 11/29/13
W moved out 12/5/13
I Retained L 2/20/14
D filed 3/17/14