How is Cole who leaves the island different from the Cole who arrived on the island?

THis depends on which time you mean. The first time Cole leaves he is barely alive and humbled. He had not quite made sense of what he had experienced though. His second trip to the island is when most of his growth takes place. By the end of his second trip, Cole is much more self-aware. He sees the bigger picture and how he may better contribute to circle of life rather than impede it.