I think all of the Dashwood’s were introduced and the condition of their hearts literally revealed to the good or evil by the narrator while we are left to judge Willoughby’s heart along with the Dashwood ladies—really to evaluate him on the same appearances, manner, behavior and speeches available to them. At most the narrator reveals Willoughby’s willingness to change his tastes at Marianne’s persuasion and suggests (as Barbara pointed out) that “any young man of five-and-twenty must have been insensible indeed, not to become an immediate convert” in Ch. 10. At least I do not recall any other allusions to Willoughby’s inner-workings or revelations by the narrator on this score but I am amiable to be corrected. (:D) There are two points of view to consider—Marianne’s & Mrs. Dashwood’s and Elinor’s. The first consider his attentive behavior a perfect representation of his heart and intent (as Elbe pointed out) while the second desires the assurance of open declaration. Nice topic, thanks! (:D)