Prince Nolan and the Missing Dragon by Ruth Pietras
 
A dragon has gone missing.  A princess is broken hearted. A young prince sets out to find the dragon.
Despite several cases of mistaken identity and disappointment, he never gives up. Finally the prince finds the dragon only to discover he is in hiding and has no intention of returning to the castle. He befriends him and learns why the dragon has run away. With the help of the prince the dragon learns
how to compromise and take turns, and with his problem solved, they happily return to the castle. Once reunited with the princess the three become life-long friends.