The ending is like one of those dark chocolate bars: bittersweet, equal parts happy and sad.
This whole time we've been waiting alongside Leigh for Dad to call, write, show up, anything—just so long as he reaches out to Leigh and acts like a real dad.
Suddenly, in the last chapter…there's Dad. Isn't this just the best?
Unfortunately—and realistically—not everything ends well. Yes, Dad's there, but he's still the same guy he's been the whole time.
Dad does find and bring Bandit home (that's the sweet part), but Leigh realizes that Bandit is not going to be happy in their little house. He also knows Dad will be lonely without Bandit, so Leigh says goodbye to his dog. Again. (That's the bitter part.)
What's up with the ending is that it shows us how Leigh has grown up. He's able to give back Bandit because he puts Dad's needs for company above his own wish to have his dog back. He knows Bandit wouldn't be happy at home alone for so much of the time, too. Being able to make that sacrifice is a real sign of maturity.
More important, though, is that he's come to accept his dad for who he is—someone who loves him but isn't the most reliable or thoughtful guy in the world. That's not the happiest ending, but it's the reality and Leigh has learned to accept it.
Break out the chocolate, please.