LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
Cassie comes back, but Evan is gone, although he left his rifle and backpack. Cassie grabs her own M16 and heads off to find Sammy, prepared to shoot anyone she sees. As she’s walking, she hears someone call her name and fires a clip of ammo in that direction but misses. Evan sneaks up on her and disarms her, then bearhugs her. She says to let go of her, but he says he can’t.
When Evan says that he can’t let go of Cassie, it has multiple meanings. On the one hand, it has the literal meaning that he’s afraid that if he lets Cassie go, she’ll either run away or try to attack him. But the statement also has the less literal meaning that Evan will always continue to care for Cassie, even if she doesn’t yet trust him.