Squall see the love section.
Rinoa There isn't much of a connection between Quistis and her. Quistis accompanies Squall and Zell in their first assignment to help out the Timber Owls, the resistance group. She witnesses the relationship between Squall and Rinoa develop that she decided she stay clear of their developing love.
Selphie A transfer student from Trabia Garden, she is also one of Quistis' students (however we see that in the beginning of the game, Selphie was late for class, so we don't get to see that interaction). She is one of Quistis' orphanage friends as they all realize later on. They have a pretty good relationship between the two of them seeing as how in the Garden Festival, they are interacting like girl-friends.
Irvine The ladies' man! He is extremely flirtatious when it comes to women and that is nothing different when he gets to meet the ladies of the cast. One of the orphanage children, they go back to childhood years and all realize that they have known each other much longer than they thought they do. Quistis, being the serious, mature type that she is, doesn't have much patience for his immaturity.
Zell Quistis is Zell's former teacher who thinks that Zell is... quite loud. She is the one that partnered Squall and Zell up together, maybe to increase both of their tolerences for different personalities.