Depression, or overwhelming sadness or despair is so isolating. One of the things that can happen when this sets in is a sense that no one can possibly understand what is being felt. This causes a withdrawal from the world, which while protective from the hurt of being misunderstood, it exacerbates the suffering as we no longer have the comfort of good relationships. And, the belief that we are worthless or not good enough becomes the prison bars through which we view life.
Breaking the prison of isolation is the first step. This sadness is not easily solved and requires all the courage and determination you have to throw at it. Reaching out can be that first small step.