I absolutely agree: Stevens could be a devoted and loving husband if he ever got to the point that (1) he could admit to himself that he loves Miss Kenton, (2) his devotion to Miss Kenton is now the Big Devotion of his life, and (3) he could actually communicate this to Miss Kenton in an effective manner. Which are all big ifs, and in the book he never manages to clear the hurdles, but you can see why Miss Kenton hoped he would.