Brandon in the novel would not say Willoughby had honorable intentions (marriage) towards Marianne as in S&S2 because he says the opposite in Ch. 31, ‘who can tell what were his designs on her?’ We know his feelings on the subject. Brandon saying Willoughby had honorable intent is a contradiction to the novel but I do not think it is in the movie. What the filmmakers did was put Willoughby’s claim of honorable intent (44) into Brandon’s confession because they could not work Willoughby’s confession into the film (The S&S S&D, page 272). The reason to do it is to let Elinor, as in the novel, pass on to Marianne a redacted version of Willoughby’s ‘vindication’ as it is termed in Ch. 47. The vindication is of his intent towards Marianne. In S&S2 Brandon says:

‘he did mean to propose that day. Therefore I cannot deny that his intentions towards Marianne were honorable, and I feel certain he would have married her, had it not been for -’ (The S&S S&D, page 155).

It is a truncated version of this:

I found myself, by insensible degrees, sincerely fond of her [Marianne]; and the happiest hours of my life were what I spent with her, when I felt my intentions were strictly honourable, and my feelings blameless. Even then , however, when fully determined on paying my addresses to her [propose], I allowed myself most improperly to put off, from day to day, the moment of doing it, from an unwillingness to enter into an engagement while my circumstances were so greatly embarrassed. (44)