The story behind that episode is that in past lives, the Dax symbiotic and the symbiont in the other trill in those pics were married, hence the attraction between the two. Supposedly there was a taboo on Trill against people who had symbiont who had shared past lives associating with each other, which held true in the end, but there were some interesting events in that episode to say the least. I think one of the reasons the symbionts wanted to be together was that they had never had a chance to say goodbye to each other in their past lives, but I'm not sure.