I'm pretty much in the same boat, my D will be 'final' in 2 weeks, if not signed sooner.
I too had a really big crash last week and am currently rebounding from.
I can only comment on two things you said:
1- You can not just let him go (drop him) just like that and move on, sorry I thought I could do the same with my W, didn't work and that's the crash I experienced last week, I lied to myself and said I was "over her and done and moving on happily". Now I realize, it's one finger at a time in the letting go process.
2- Yes, a piece of you is missing and will forever be should things not turn out as we all hope our situations would, that's just the way it is.
Me 35/XW 33 S13 & S12 M: 10/17/98 OM & S: 07/08 D final 06/09/09 12/03/09 - 06/13/10 "Piercing" 06/13/10: Engaged to Re-marry 10/17/10 06/25/10: Expecting baby #3 2/14/11