Despite all their bickering and incompatibility, Lavagirl doesn't hesitate to save Sharkboy from the electric eels at the risk of her own life. When Max tries to stop her, she simply responds, "He's my best friend" and dives in.
When Max's parents reconcile after they realize they can't live without each other.
Lavagirl thanks Sharkboy for saving her with a quick (but painful) kiss on the cheek. At the end they try to hold hands, but as this hurts too much, they simply settle for touching fingertips.
The implication that Shark Boy and Lava Girl are based on Max's parents.