Before my interview with Dr. Orna Guralnik, I was a little more nervous than usual. Throughout the four seasons of the Showtime docuseries “Couples Therapy,” Guralnik — or simply Orna, as she is known to the show’s participants — has a commanding and authoritative presence. Each season follows Guralnik, a New York-based psychoanalyst, and several couples over a series of sessions. As the couples, who come from a wide range of backgrounds, work through impasses in their relationships, they uncover wrenching pasts and arrive at deep emotional truths. But for many viewers, the most captivating part of the show is Guralnik’s seemingly unflappable demeanor.