Nope, it was a fling. In an early interview Andrea Thompson outed her character as bisexual, and the episode in question ("Divided Loyalties") showed Talia rolling over in bed and discovering that Susan wasn't there. In a later episode, Susan confessed to Delenn that "I think I loved Talia."
Some fans and production staff were disappointed that JMS shied away from displaying thier affection more openly, though Babylon 5's then-marginal status in syndication may have had something to do with it.