Hunger Games pt.2

Continuing from The Hunger Games,
How I annotated the second section of the book was the major events that are taking place in the chapter, so when I do come back to reading, I would remember what I read so far. I also recorded my reactions towards the events where I think I was pretty surprised with, especially with Katniss's unexpected actions.
The parts of the book I like was how clever of Katniss to ridden herself of tracker jackers by cutting their hollow nest directly below the group of candidates that were hunting her. I can tell Katniss has a good heart, despite of being one of the contestants, Rue, she was only a twelve year old, like her younger sister who was to be the actual candidate, Prim; Katniss treated her as if she was Rue was Prim. There was the time when she was going to be killed because of Peeta, but when she found Peeta slowly dying from a wound caused by a boy candidate named Cato, she treated his wound, despite of how disgusting it was or how she always stay clear from critical wounds the miners her mother would take care of.
What I was confused about was this: Why did Peeta join the group of candidates in hunting the other stray ones? Is this to hunt down Katniss? Is it because she had an eleven on her score with the Gamemakers that was the reason for his envy? How about Rue, why did she trust Katniss so much, that she willingly accepted Katniss's invitation in teaming up with her to defeat the career candidates? Was Katniss that trustworthy in your opinion?
Other than that here's more questions: What do you think about Peeta's actions? Is it wise for Katniss to trust Rue and Peeta again despite of his betrayal?