Sadness will not kill you. Depression won’t either. But fighting it will. Ignoring it will. Trying to escape it rather than confront it will. Denying it will. Suffocating it will. Allowing it ni place to go other than your deep subconscious to embed and control you will. Not that you’ll take your life or destroy everything “good” you do receive (thought you might) 

BUT, it will kill you in that it will rob you of every bit of life you do have. You either let yourself feel everything or numb yourself into feeling nothing. You cannot select emotions. You are either in accord with their flow or in resistance to their nature. In the end, the choice is yours.