Disappointed of doing her a service. How else could he be disappointed?

“It won’t break my heart,” laughed Eugene; “it won’t stay by me eight-and-forty hours; but I am genuinely disappointed. I had set my fancy on doing this little thing for you and for our friend Miss Jenny. The novelty of my doing anything in the least useful, had its charms. I see, now, that I might have managed it better. I might have affected to do it wholly for our friend Miss J. I might have got myself up, morally, as Sir Eugene Bountiful. But upon my soul I can’t make flourishes, and I would rather be disappointed than try.”

If he meant to follow home what was in Lizzie’s thoughts, it was skilfully done. If he followed it by mere fortuitous coincidence, it was done by an evil chance.