and there's definitely a very good time to confess.

My post above was to highlight the extent to which Willoughby went to avoid the Dashwood sisters, and all their common aquaintances.

*Then* would have been the best time for any confessions. He isn't married yet, so any sentiments of affection expressed towards Marianne wouldn't be as inappropriate as they were when he *did* confess at Cleveland.

He didn't even have to do it in person, because as Elinor said for a previous similar occasion (of confessions);

"Why did you call, Mr. Willoughby?" said Elinor, reproachfully; "a note would have answered every purpose.

He is getting married and the decent thing to to would be to tell her that. The right kind of confession, which would bring some kind of closure to all parties concerned.
We know how she suffered in her anxiety. How this whole thing ended in shock and humiliation.
All this could have been avoided.

But as Willoughby says;

All that I had to do, was to avoid you both. I sent no answer to Marianne, intending by that means to preserve myself from her farther notice;

He certainly preserved himself well causing Marianne a lot of heartache during that time of uncertainty.

Again, a note would have answered every purpose.

So why did he not confess about his plans then?
Is it because it isn't in his character to explain anything to his castaways, same as he feels he owes nothing to his child and Eliza?

The answer to this is interesting, again according to ones interpretations.
Why he confessed later on is clear and has been discussed in detail.