Many individuals consult selected doctors on a regular basis. Inevitably, a relationship eventually evolves, albeit a strictly professional one. The doctor and yourself must guard the limits of such a relationship to strict professional boundaries. If certain lines ever get crossed, the relationship becomes something else, and can no longer be defined as a doctor-patient relationship.
Medical practice is bound by strict ethics, which doctors must uphold at all times. Patients too are bound by unwritten social norms and behaviour. It is thus a two-way process that inherently protects the relationship with your doctor from veering off the professional path. But inappropriate social relationships between doctors and their patients are not unheard of. The extreme is when such relationships become sexual.