From your description it seems that he is suffering from psychotic illness (most probably Schizophrenia) and not Depression. You should ask exact medical diagnosis to treating Psychiatrist, major psychiatric problem is a vague term. If it is Schizophrenia then ask about prognosis (i.e. outcome). Schizophrenia is chronic disorder and gives life long ailment. You have to live with his oddity. If you are mentally prepared for this then go on. ( You should also discuss this issue with treating psychiatrist in his absence).
His sexual problems may be a part of an illness or side effects of medicines. However you can not afford to stop medicines with out psychiatrist’s advice.