Talia and Susan
At the opening of the first series, Lt Commander Susan Ivanova is the second-in-command and in charge of day-to-day operations at the space station, Babylon 5. Talia Winters is the resident telepath, on assignment from the Psi Corps. Following Talia's arrival on the station, Susan attempts to avoid her. Talia, however, persists, and when she seeks Susan out at the bar after work, Susan explains that her mother had been a latent telepath who had been forced by Psi Corps to take drugs to suppress telepathic abilities. This had led eventually to her mother's suicide, and left Susan with a deep dislike and distrust of the Corps (Episode 1: Midnight on the Firing Line).
Talia's loyalty to the corps remains a barrier between the two women. Their differences show for example when a young girl on the station suddenly shows evidence of telepathic ability. Talia wishes her to join Psi Corps, while Susan swears the Corps will not take her from Babylon 5 (Episode 17: Legacies). Nevertheless, Susan admits that she finds Talia an 'interesting person'; and when Talia becomes the sole witness to a murder on the station, Susan advises Captain Sheridan that he can trust Talia (Episode 28: A Spider in the Web). Talia is also exposed to evidence of corruption in Psi Corps when her former lover, Jason Ironheart, appears on the station, pursued by the Corps. Psi Corps experiments have increased his telepathic powers exponentially, and he has come to bid Talia farewell, before he is transformed into a new kind of telepathic being (Episode 6: Mind War).
The barrier is finally broken down when Talia is asked by the Corps to investigate an 'undergroud railroad' of unregistered telepaths. Talia is captured by a group of the telepaths;
once she has heard their stories, and discovered their links with Jason Ironheart, she decides she cannot turn them over to the Corps. Having helped them outwit the Psi-Cop Bester, Talia arrives at Susan's quarters late in the evening, telling her that "in light of recent events, I think we need to reevaluate our relationship. Which is just a formal way of saying that I needs someone to talk to, and, strange as this sounds, you're the only one I can think of" (Episode 30, A Race Through Dark Places).
From this point there is a growing friendship between the two women. Although it is not explicitly stated in the show, it is suggested that this friendship blossomed into a physical relationship in Divided Loyalties (Episode 41), when Talia shares Ivanova's quarters. We see her waking in the night and reaching across the bed to find Ivanova missing.
However, the relationship is cut short when telepath Lyta Alexander returns to the station, warning that there is a Psi Corps 'mole' on Babylon 5. Her telepathic scans trigger a buried personality that Psi Corps had implanted within Talia. Lyta's scans also reveal that Susan herself has latent telepathic abilities, which she has long attempted to keep secret. When Susan approaches the new 'Talia', hoping to reach some part of her old personality, 'Talia' tells her that she had manipulated their relationship in order to get closer to Susan and the information she had access to. Susan leaves, telling her that 'the Talia I knew is dead'. 'Talia' then returns to Earth. The truth of this relationship is not revealed until Delenn initiates a 'rebirth' ceremony on Babylon 5, during which Susan confesses to her, "I think I - loved - Talia" (Episode 55, Ceremonies of Light and Dark).