Why did Pony that Darry hated Paul Holden?

Darry steps foward to start the rumble off, saying that he'll take on any of the Socs. Paul Holden steps forward from the Soc side; he is one of Darry's ex-friends from high school, and now he looks at Darry with a mixture of contempt, pity, and hate. Ponyboy realizes that Darry is not only jealous of Paul and the opportunities he has that Darry doesn't, but he is ashamed to be representing the Greasers. The two young men start to circle each other in the silence, and Ponyboy thinks about how they shouldn't hate each other.