Complex sentence: Miss Clavel assures Madeline that whatever happens, they'll be together but this is denied by Covington who says that Madeline is right and wishes he could do something about it but has already sold the school.
Split into simpler sentences: Miss Clavel assures Madeline that whatever happens, they'll be together. But this is denied by Covington, who says that Madeline is right, and wishes he could do something about it, but has already sold the school.