Shakespeare's Sonnets: My love is as a fever longing still

My love is as a fever longing stillFor that which longer nurseth the disease,Feeding on that which doth preserve the ill,Th' uncertain sickly appetite to please.My reason, the physician to my love,Angry that his prescriptions are not kept,Hath left me, and I desp'rate now approveDesire is death, which physic did except.Past cure I am, now reason is past care,And frantic mad with ever-more unrest.My thoughts and my discourse as mad men's are,At random from the truth vainly express't, For I have sworn thee fair, and thought thee bright, Who art as black as hell, as dark as night.