Leaving alone is no solution for a case of depression or anxiety, person may become more aloof or may harm oneself as well... sticking too much might cause frustration and irritability in the person with might result in anger outbursts and harming others or property... best is to take help of an expert (psychiatrist) to confirm the diagnosis and to start appropriate treatment. If they are feeling weak to discuss their own problems, a therapist may help them verbalise their issues and to deal with them in an appropriate manner...