While we all love to fantasize that Mrs. Willoughby nee Grey plagued Willoughby's heart out, the author tells us in the final chapter of S&S that this was not the case. I don't think that the Willougby's belong in the Bad Marriage Top 5.

"...But that he (Willoughby) was for ever inconsolable -- that he fled from society, or contracted an habitual gloom of temper, or died of a broken heart, must not be depended on -- for he did neither. He lived to exert, and frequently to enjoy himself. His wife was not always out of humour, nor his home always uncomfortable! and in his breed of horses and dogs, and in sporting of every kind, he found no inconsiderable degree of domestic felicity."