It's hard to imagine that bitter-sweetness he must've felt. At the same time, how could he ever complain. Maybe he took no issue, but I'm sure everyone in the program was hoping to be the first man.
I forget the exact wording in his autobiography but it was something like "I can't pretend I'm crazy enough to prefer being in my seat to the other two's. But I've got my own part to play."
They are also cut-throat competitive, ego maniacs. Just incredibly professional. I don't think you get to where those guys are without an incredibly appetite for success.
That's the central thesis of The Right Stuff. Collins was bumped from Apollo 8 and didn't feel that bad about bumping someone else from Apollo 11 as a result.