I went back and re-read ch.31 though the Colonel made me cry once this week already.

I still don't know the answer to your question. Reeba makes a good point though.

What I found was that even after Willoughby's engagement to Miss Grey became public, Colonel Brandon still struggled and didn't know if he should tell them.
"...I think I am justified -- though where so many hours have been spent in convincing myself that I am right, is there not some reason to fear I may be wrong?" He stopped.