Lulu didn't get married to Chappu (Wakka's Brother) and she had to get married, right? So instead of marrying a family friend, she married Wakka. Wakka thought that Lulu married him because he thought that she liked him, but he finds out later on in Final Fantasy X that she married him in a form of apolgy. Go to this little hidden section a little past the lift (don't go on the lift) and you will see Luzzu and Gatta arguing. After that, talk to Luzzu again and the scene will occour about how that happened.
P.S. If you want Luzzu alive use Seymour's Overdrive and if you want Gatta alive, don't use Seymour's Overdrive. It is really really hard to get Seymour's Overdrive up since it only goes up when the boss does Demi.