"I did know Rue. She wasnt just my ally, she was my friend. I see her in the flowers that grow in the meadow by my house. I hear her in the Mockingjays song. I see her in my sister, Prim. She was too young, too gentle. Im sorry.
This scene actually happened in the movie only not in the Book . However in the book Peter was not weak either . He seriously would do anything for Katniss. And if he were weak he wouldn't survive Book 3 .