Why did Soda bolt from the room when Ponyboy and Darry were arguing?

In chapter 12, Soda comes in from work, asks for the mail, then flops down on Pony's bed and begins smoking a cigarette. Ponyboy can immediately tell that something is bothering Soda, who insists that he is fine. Later that night, Darry and Ponyboy begin arguing over Pony's failing grades. Pony mentions that this is their fourth argument of the week, and Darry tells Ponyboy that he has been living in a vacuum. In the middle of their argument, Pony looks at his brother and mentions that Soda has a pained expression on his face. Soda then says, "Don't... Oh, you guys, why can't you..." (Hinton 148). Soda ends up running out of the house, and Darry informs Pony that Sandy broke up with him, which explains Soda's sensitive mood. After Pony and Darry chase down Soda, he tells them that he cannot take them fighting with each other anymore, which is why he ran out of the house. Soda feels like his brothers are playing tug-of-war with him and finds it difficult to pick sides. Pony and Darry then apologize for fighting and promise that they will try getting along.