After Nemo is rescued, Dory is caught in a net and is almost taken away. Nemo tries to rescue her, and at first Marlin says no, but then let's Nemo go save Dory, to show that he now had faith and trust in his child and has outgrown his fears of the ocean.
Marlin realizes his mistake. He apologizes to Nemo for not believe in him. Marlin learns to let go and believe that all will work out in the end.
Marlin returns home with his son. He let's Nemo enroll in school and lives a more relaxed and happier life