Gandalf Vs. The Witch King

[Guinevere]

Can it be that the staff-breaking could have affected Movie-Gandalf's state of mind ?
Because in the "Last debate" scene afterwards, he acts totally out of character.

Gandalf: "Frodo has passed beyond my sight. The darkness is deepening."
Aragorn: "If Sauron had the Ring, we would know it."
Gandalf: "It's only a matter of time. (.........)
(.........)
Gandalf: " (.....) I've sent him (Frodo) to his death"

I could hardly believe my ears!! What's happened to Gandalf, the kindler of hope, whose credo used to be "Despair is only for those who know the end beyond all doubt - we do not." ? Gandalf may be afraid, yes, but never hopeless and despairing!
Why did they have to change the person of this central character so much ? Perhaps to make a contrast for Aragorns sudden hopefulness and resolution ? In this movie scene, the "diversion" is Aragorn's idea and Gandalf doesn't even believe it'll work!
I really don't mind obliterations and changes that are "in character" (like many in FotR) but this is too much!