... in some respects. (Ducks rotten tomatoes!)

(1.) I think his unhappiness is genuine. Towards the end of Ch.44, a paragraph of Elinor's silent thoughts about Willoughby's situation ends with:-

"From a reverie of this kind she was recalled at the end of some minutes by Willoughby, who, rousing himself from a reverie at least equally painful, started up in preparation for going"

The part highlighted in bold is the narrators voice rather than Elinor's impression, so I think it is intended to be read as a straightforward statement about how he is feeling.

(2.) I think his remorse and regret are genuine. He is really sorry that he is stuck in a situation in which he is unhappy. I don't think he feels any remorse for making others unhappy except as it impacts on himself.

(3.) I think the whole of Willoughby's confession is genuine in the sense that it is the truth as he sees it. He has been mulling things over in the five months since he left Barton, so his perspective has altered, and he has adjusted his internal narrative so as to feel a little more comfortable about what has happened. It is also a partial version of the truth, omitting some elements of what happened (such as the duel, and hypothetically his feeling of being humiliated by Col. Brandon) but I don't see evidence that he is consciously telling lies.

It seems to me that Willoughby's wish for 'forgiveness' is in effect him wanting to be given permission to feel ok about himself again. If he had concocted a deliberate tissue of lies then the resulting 'forgiveness' would be meaningless. I also think he would have edited more. Ironically, his confession actually gives the reader and Elinor insight into some of the uglier aspects of his thought processes, which I don't suppose he intended at all!.

4. Following on from (3.) I think he is telling the truth when he says he was "sincerely fond" of Marianne. As to whether he meant to marry her, it seems credible to me that he eventually liked her enough to wish to marry her, though I suspect that any settled intention of actually proposing lasted no more than a few days. The extent of his fondness and wish to marry her have very likely become inflated inn his mind with the passage of time and the knowledge that he can't have her (wanting most what he cannot have).