Leaving

Perry, glad to be out of Kansas, at last relaxed. Now it was true--they were on their way-- On their way, and never coming back--without regret, as far as he was concerned, for he was leaving nothing behind, and no one who might deeply wonder into what thin air he'd spiraled. The same could not be said of Dick. There were those Dick claimed to love: three sons, a mother, a father, a brother--persons he hadn't dared confide his plans to, or bid goodbye, though he never expected to see them again--not in this life. (Capote 106)

Perry and Dick have distinctly different views of leaving after completing their plans. Their lives are completely different in general.

Dick has family "three sons, a mother, a father, a brother" to leave behind. These things are important to him. Part of him wishes he could "confide his plans" to these people or at least "bid goodbye." When he leaves, he will miss these people. Plus, he doesn't have some deeper need to leave behind his life other than to run away. This is very important because he will never be happy in his new life.

Perry on the other hand is living out his dreams. He always planned on going to Mexico or some other exotic place. He is "glad to be out of Kansas" and leave behind what they did. "He was leaving nothing behind" in the first place. He is happy to be "on their way" to his new life.

If one isn't happy, this 'new life' will fall apart and ultimately their getaway will fail.