Book Three of the Prydain Chronicles by Lloyd Alexander
In THE BLACK CAULDRON, Taran had to learn to deal with the nasty, mean-spirited Ellidyr. In THE CASTLE OF Llyr he has to learn to deal with a nobleman who is a doofus. A nobleman who is a doofus who is also to be betrothed to Eilowny, Taran's beloved. So no matter how strong and brave and honorable Taran is, he believes all of those qualities to be trumped by an idiot who happens to be high-born. He must learn that "For a man to be worthy of any rank, he must first strive to be a man."
This book doesn't speak to me the way the others do, however, I know it is necessary in the scope of the series. Fflewddur gets his giant cat, Llyan. Eilowny is almost lost to Taran, but at the very end of the book, the reader is sure they will be reunited. And Taran seems to be done looking to others to discover who he really is and what he will really be. He is ready to look within.