Technically it couldn't have destroyed Rey's personality, he had none to begin with. Every episode he either uses one or two word responses or yells at Lunamaria in the middle of combat. This episode was the most we've ever seen out of him. The Lacus x Athrun engagement is left over plot from SEED. Lacus and Kira only got together really after Lacus had already left PLANT, so the majority of the masses know nothing of Athrun's relationship problems with Lacus. As far as they know, Lacus and Athrun were always an item.