Character development is having a character who would previously deny all negative feelings, and completely refuse to tell anyone or fully acknowledge that they're depressed... Do exactly that. And then proceed to try and talk more about their feelings, so they can be comftorable talking about it with a therapist.

Character Development can also be having a character who tried seeing the best in everyone react differently to the general populace due to previous experiences that kept piling up.

Regardless of how that character changes, for the better or for the worst, they still changed. And that is called Character Development.