about Isabella and Capt Tilney in the conversation with Catherine in chap 19? When Cath said James was very uncomfortable, Henry responded --

'“Is it my brother’s attentions to Miss Thorpe, or Miss Thorpe’s admission of them, that gives the pain?”

“Is not it the same thing?”

“I think Mr. Morland would acknowledge a difference. No man is offended by another man’s admiration of the woman he loves; it is the woman only who can make it a torment.”'

Henry was trying to tell Cath that Isab may not really care for James, though he could not say that outright.

Catherine did get some inkling -- she 'resumed with, “Then you do not believe Isabella so very much attached to my brother?”

“I can have no opinion on that subject.”

“But what can your brother mean? If he knows her engagement, what can he mean by his behaviour?” .....

"My brother is a lively and perhaps sometimes a thoughtless young man ... "'

I suppose Henry felt he had said as much as he could about Isab not really caring for James, and that lively, rather thoughtless Capt Tilney was amusing himself with a light flirtation with an engaged woman he had no serious intentions towards.