Why is Cherry so worried about Ponyboy? Why does she keep coming around? What significance does her talk with Ponyboy have on his feelings about the rumble?

At the beginning of the novel, Ponyboy and Cherry meet each other at the drive-in and have a meaningful conversation. They share a connection while they are discussing sunsets and the two characters become friends. After Johnny kills Bob Sheldon in self-defense, Cherry tells Dally that she's willing to be a spy because she felt that the whole thing was her fault. She tells Dally that she is willing to testify and will give him updates before the rumble.
In Chapter 8, Cherry meets up with Ponyboy and tells him that Randy will not be going to the rumble. She also tells Ponyboy that she won't see Johnny in the hospital because Johnny killed her boyfriend. Initially, Ponyboy is upset that Cherry refuses to see Johnny. Then, Cherry tells Ponyboy that she wasn't helping them because she felt sorry for him. She also tells Pony,

"I liked you from the start... the way you talked. You're a nice kid, Ponyboy. Do you realize how scarce nice kids are nowadays?" (Hinton 110).

Cherry is simply concerned about Ponyboy because she views him as an understanding friend. The reason she keeps coming around is because she feels partially responsible for what happened to her boyfriend. Their conversation makes Ponyboy reflect on his actions, and he begins to wonder why he is even proud of being a Greaser. His heart is not in the rumble and he realizes that violence is useless. The only reason Ponyboy participates is because he is a loyal friend.