Jackson and Serenity were back together again. Why did that upset Lucas so much?

When Jackson hugged Serenity earlier, Lucas felt so jealous that he wanted to pull them apart...

Suddenly, Lucas heard a voice asking, "What's gotten into you just now?"

He looked up and saw that it was his childhood friend, Caleb Moss.

"You're here too," Lucas said.

"Yeah. When I saw you and Jackson earlier, I wanted to come over and say hi, but I quickly realized that the mood here was weird," Caleb said.