Which line from Extremely Loud and Incredibly Close reveals a despondent tone?

I zipped myself all the way into the sleeping bag of myself, not because I was hurt, and not because I had broken something, but because they were cracking up.

This lines hows despondent tone

Explanation:

Despondent is in depression from loss of hope or spirit feeling or showing profound despair, dejection, discouragement, or gloom:It is tone showing fully depressed hopeless or in gloom or having no courage.

I zipped myself all the way into the sleeping bag of myself, not because I was hurt, and not because I had broken something, but because they were cracking up.

This is the line that reveals a despondent tone.